Nowadays, a small party of adventurers rides off alone into the wilderness, then ties up their horses at the dungeon entrance and heads on down without a moment's thought to logistics and then maligns their killer DM when the party wipes. Or else all concern for resource management is hand-waved away and the PCs carry on indefinitely with their adventures, never stopping to tally up the load - which probably comes to thousands of pounds per character.
Sometime betwixt then and now, D&D transformed from a game of exploration into a game of heroic fantasy. In heroic fantasy no one ever worries about trivialities such as having enough food or supplies, nor how many silk tapestries or iron-bound chests one person can reasonably carry. The shift has been gradual, and I'm not sure exactly when it started. Hirelings were definitely an important part of AD&D (1st edition, at least - I missed 2nd edition entirely). 3E has rules for hirelings, but I never once saw anyone actually use them, and 4E has cut them out of the game entirely.
My guess is that once D&D adventures started to become more about big meta-plot stories, henchmen and hirelings fell by the wayside since planning and logistics are largely unnecessary when participating in a pre-scripted storyline. This is just speculation, though, somehow the shift in play style occurred gradually enough that I didn't even notice. I just woke up one morning and said, "Hey, where did all the hirelings go?" Their absence is a glaring reminder of how much the assumptions about our hobby have changed in the last few decades.
I think a dungeon adventure should be more like a real-life expedition; well-equipped, well-manned, and well-organized. Look how many people it takes for a couple of people to make it to the summit of Mt. Everest. There aren't even any monsters after them, and they aren't collecting any treasure, but they still have a small army of porters and cooks to provide logistical support. Look also at some of the great expeditions of the early 20th century, made by museums such as the American Museum of Natural History, to remote locales such as Mongolia and Antarctica, which were led by just a few key individuals supported by a large number of support personnel.
I envision a well-organized dungeon expedition arriving at the site and establishing a well-guarded base camp to serve as a secure place to rest, recuperate and drop off treasure, followed by a thorough reconnaissance of the local area to assess the threats prior to descending into the depths. This will take enough mercenaries to adequately guard the base camp, plus a few more to accompany the exploration party into the dungeon. You'll also want enough porters to carry all the dungeon gear that you might need - rope, iron spikes, crowbars and hammers, ten-foot-poles, etc., are all bulky, heavy things. If the PCs try carrying all that stuff in addition to their armour and weapons they won't be able to move, let alone bring any loot back. Torch-bearers are important, too. Bring lots so that one mishap doesn't leave the party in pitch darkness at a critical moment. While we're at it, why not hire some specialists as well. You never know when a sage might come in handy to help decipher the ancient runes you've found all over the ominous looking Portal of Obvious Plot Device. Hirelings are cheap. Bring lots.
I've been slowly trying to introduce henchmen and hirelings to my game, but it has been difficult to overcome the inertia of years of hireling-free play. My hints and suggestions were, at first, completely disregarded and it wasn't until I switched to Swords & Wizardry, which includes hirelings in the equipment list that the players realized: "hey, we can hire help!" I interpret this as the natural reaction of players to assume that any advice the DM offers is just a devious scheme to screw them over and should be ignored unless it actually appears in the rules. Even still, it was hard to overcome player paranoia enough to get them to actually shell out the silver piece for a hireling. As one player put it, "they're just going to betray us." And so they might - if they aren't treated well. But there is no reason to assume that a well-compensated lackey won't provide reliable service.
So the first attempt to hire lackeys was conservative, to say the least. The party hired a couple of mercenaries to help fight and one guy to hold the torches and carry all of the gear. He looked like this:
This is an absolutely fantastic Reaper miniature that I fell in love with the moment I saw it. He really exemplifies the much-maligned dungeon porter and I can't help but chuckle every time I look at him.
From a DM's perspective, hirelings are great because you can show off how lethal and scary your new monster is by having it eviscerate a convenient hireling - this way you don't have to kill off a PC just to set the mood.
Now, as I mentioned, hirelings that are well-paid and cared for can usually be relied upon to provide loyal service, but even if the PCs are a bunch of tight-fisted callous bastards, they'll still find hirelings indispensable resources. One of my favourite literary examples of this is Alexandre Dumas' The Three Musketeers. Each of the Musketeers has his own lackey and they are quick to encourage young d'Artagnan to acquire one as well. If you've ever read the novel (and if you haven't, you should) you'll know that the musketeers are perpetually short on funds - they are in debt to their tailors, and landlords, and rely upon cadging free meals from acquaintances. Yet they still retain lackeys who seem never to be paid, nor particularly well treated. They are forced to sleep on the floor and are given a sound thrashing when their morale begins to wane. Whenever the musketeers do come into money it is spent on wine and getting back into the good graces of their tailors. The lackeys never get paid - yet they remain faithful and loyal servants, which is probably a commentary on living conditions in 17th century France.
Even the most dick-headed employer can find good use for disposable employees:
|"I think we should let the diggers open the case"|
Let's not forget about Henchmen. The good old henchman is your personal sidekick; the Robin to your Batman, and can be counted upon to provide good and loyal service and is even competent enough to kit out with high-end gear and be kept happy. Still, there are occasions, like when you need someone to do a job, like align a communication dish in an alien-infested complex, that is just too dangerous for a PC:
|"Yeah, man, Bishop should go!"|