There is strength in numbers in many cases for obvious reasons, even for pacifist challengers: More treasure can be carried away, varied skills and abilities only certain characters have can be used together, and (of course) the more allies are with you, the more "moving targets" there are for the bad guys to take a shot at without scoring a "kill" of their own.
There is a major disadvantage of doing this though:
Pacifist challenge players who can't kill things to gain experience points face a scarce finite supply of experience points, the majority of which are only available through nonviolent questing.
This is also the case in a lot of other games, but in Baldur's Gate (following D&D tradition) the scarce experience points you receive are automatically evenly distributed between every single character you have in your party at the time they're awarded. (In other words, if you receive 500xp and have 5 characters in your party, each one only receives 100xp each— whereas if you were doing a solo run with only one character, that character would get all 500xp for themselves.)
This makes bringing allies with you very costly, but there is one twist you can use to your advantage:
A player can recruit NPC allies and being them along, and then (anticipating the ending of a given quest) can politely ask other party members to temporarily leave the party, so that only active members of the band receive the XP when the quest is solved. Then they can just talk to their old ally again and re-recruit them right afterward.
Pacifist run players who don't kill anyone or anything for xp can bring NPC allies with them for as long as they want without a penalty, since no one gains xp from "kills" in the first place.
This is arguably not an unfair "exploit", by the way, since the party members excluded from the band don't get any XP at all and therefore can't be leveled up past whatever level they began with (unless you cut them in on an equal share of the xp elsewhere).
It's just a somewhat odd way of distributing scarce xp to where it's going to be most effective: Either entirely to your own player character, or split just a few ways between the team members with the skills that most urgently need to be leveled up.
This especially useful in some cases where you need to rescue characters from dungeons and bring them to safety, but then ask them nicely to wait outside the band rather than stealing your xp when competing quests.
Another big advantage is that you can also bring a strong fighter-type character or two, cast invisibility on them, and convert them into pack-mule-like allies who can carry over 100 pounds of treasure away while you're nonviolently looting enemy strongholds. (The invisibility spell will only be cancelled if the strong characters tried to grab the treasure themselves, but you can use a thief or mage to pass it off to them without breaking the spell cast on the NPC ally.)