The more I think about it, the more I think that there should be a lot more NPCs going along with the PCs when they adventure. You can feel free to disagree, but first, read my Tricks and Traps blog post.
But what else are these NPCs doing? I think that depends on your party. Most of the Wild West movies that I love involve them hiring a tracker. Unless someone in the party is really a skilled tracker (and you probably want them to be really skilled killers), then you probably need to hire a tracker in order to go after guys when you don’t know where they are. I often complain about sages and scribes telling the adventurers about mystic treasures and then trusting said adventurers to go off and retrieve this one of a kind historical item while the scribe sits at home and waits. Not to imply that scribes like exploring dangerous ruins, but to determine the location of a historic treasure and then trust the safe retrieval of this historic treasure to a team of thugs and murders - really? The scribe guy doesn’t want to go along? What if there’s a fake historic treasure and the “dumb” adventurers grab that because they don’t know any better? What if there are additional historic treasures that they may not recognize? What if they break it? What if they steal it?
I’ll go down this rabbit hole further: While you might expect your roguish guy to be able to pick the lock on a standard treasure chest (or bash it open), is your lock smith really good enough to beat a lock that has kept treasure hunters out of a tomb for centuries? Is your priest(ess) good enough to scare off the undead that have protected their final resting place? Your warriors may be tough enough to take on a dragon, but if some trap maker built something that can take them alive, are your warriors technical enough to use the trap properly?
I think adding NPCs in this fashion works best when you know a little bit about what you’re going to face. My parties know relatively quickly when they need to get on a boat to get where they’re going. So are the sailors all NPCs who are going to fight during this mission? Probably not, unless they get attacked at sea while they’re getting there. Otherwise it’s drop the party, then pick them up and head home. The NPCs I’m talking about now are just a little more than that. How about examples?
The party knows that there is a vault door, so they bring a safe cracker. They know there is a chasm because the bridge collapsed decades ago, so they bring a conjurer who can conjure a bridge, or a sorcerer who can fly them across. They know they have to scale up or down a cliff, so they bring a professional climber. The bandits were not at their “regular” camp site, so they bring a tracker. The hellhound with the flaming breath is in the jungle, so they bring a guy who flies to act as a forward scout. All the signs in the ruined castle are written in an ancient language, so they bring a language expert to translate. The dwarves between here and there are friendly, but only if approached in the right manner, so they bring a dwarven ambassador.
This isn’t Ars Magica where you bring a bunch of NPCs along to kill off along the way. This is an intelligent approach to “professional” adventuring. You might even want to think about it as Mission Impossible. Sure, you have Tom Cruise along on every mission, but he needs certain types of support along the way. Please help me by coming up with a better analogy than that!