Is there a point to saving prisoners that aren't my target?

In MGS5 Ground Zeroes' first mission you're tasked with finding and bringing back Chico. In the prison camp there are four more targets. Do I bring them all or just Chico? Does it matter? Does it help towards any achievements?

For that particular mission, you only need to rescue Paz and Chico.

However, rescuing prisoners grants you points, which all count towards your mission grading. Each prisoner grants you 3'500 points, Paz and Chico included. If the prisoner dies, e.g. when you're being shot while carrying them, they will not grant you any points.

Getting an S-rank can be really difficult in some missions, unless you rescue a few prisoners. Of course, you'll need an S-rank in every mission, Side Op, and Extra Op if you want the Hero Trophy/Achievement.

There is one prisoner, who isn't among the 5 from the Old Prisoner Camp, whose rescue grants a Trophy/Achievement, notably the Rescue one.

Once Chico has been extracted, and you're heading back to rescue Paz, you'll find 2 soldiers talking about a prisoner who attempted to escape and is now going to be executed. You can either follow the one, who then leaves, or you can simply threaten him into telling you where that prisoner is being held.

During Side Ops, some prisoners may give you a tape when rescued. These are necessary for unlocking the Information Trophy/Achievement. For instance, in the "Destroy the Anti-Air Emplacements" Side Op, there is a member of the MSF held in the same place, where Paz can be found during the "Ground Zeroes" mission; he will give you a tape after you extract him.