Another "man-monster", bandits to me really reinforce the relative differences between adventurers, monsters and normal men as discussed in the excellent post by JB on B/X Blackrazor.
We are told that bandits are NPC thieves that have banded together for the purpose of robbing others. Looking at the entries for bandits and normal men we can see that bandits have on average nearly twice as many hit points and are +1 better to hit compared to normal men. Their dangerous and nefarious lifestyles make bandits far more dangerous than normal men. The average farmer would be terrified of a group of bandits as they could easily take what they wanted and kill him and his family.
We are told that bandits have a leader that can be of any class. This leaves open many possible adventure hooks. A bandit group led by a magic-user could have very different goals than one led by a cleric or thief.
Looking at the Wilderness Encounter Table - Subtable: Men on page X57, bandits can be found in nearly all terrain types, except desert and ocean where they are replaced by dervishes and pirates respectively. Bandits are more likely to be found in "Inhabited" or "City" areas which makes sense since you need other people to rob.
In my games, bandits are often one of the most common monsters.
I would like to come up with an adventure hook involving a group of bandits led by a cleric that are hiding out in a jungle.