Recruits are people who have survived on the surface against all odds through the nuclear war and are not originally in the family. They can be recruited (hence the name recruits) to do tasks the family would otherwise do, i.e. scavenging and defending the shelter, because you will lose if you lose all four family members. They have a loyalty bar instead of a trauma bar, which goes up as the days pass. Once loyalty is at the maximum, then the trauma bar will take its place. Once the loyalty bar gets high enough, they will be able to go on missions outside of the shelter.
It is better to have a possible recruit come into the shelter rather then being found outside because they will most likely have much better attributes.
Some recruits will actually kill a fellow person in the shelter if a weapon is accessible and nobody else is in the shelter. Prior to this, they will leave the shelter. Once the recruit is loyal however, this will never happen, and the survivor will become able to go on expeditions either by themselves or with the family.
If you want to have less recruits, you may kill them off rather then dismiss them, because when you dismiss them they will either steal or break something in the shelter. However, doing so will cause trauma to all other shelter members.
When a shelter member dies, a recruit may leave if they aren’t loyal enough.
Recruits are more preferable to send out to kill more dangerous enemies such as the protection racket boss, or the more deadlier factions such as the Marauders or the Corps. By the time the deadlier enemies have appeared, the player will likely have trained them up and collected plenty of guns, ammo and explosives for the recruits to use against them. Family members, whether they are the starting characters or those met in Extended Family, are more important to keep alive and can still die permanently...