You must also remember that there is a distinction to be made between the photos taken by the photographers for the FSA and those taken for themselves during their trips around the USA for the FSA. As mentioned, Stryker had pretty precise ideas of what he wanted to document and, even more important, how he wanted it documented, even though he did understand each photographer's particular interests. All the photographers complied and sent in their assignments, but that didn't prevent them from taking a bunch of photographs of the same subjects in their own, developing style.
That's why it's not always easy to know if a pic is a FSA photograph or one done during a FSA trip.
The photos had a wide variety of functions. Here's an excerpt of a Roy Stryker letter to Walker Evans that'll give you a taste of what he was after:
Tupelo - The projet at Tupelo is being returned to local management. There is an insistent demand here for additional photography to be used for publicity purposes, so it is absolutely essential that yolu get in and take a set of pictures showing the present state of the buildings, and some additional local color, also people and activities. I would suggest that you make two Leica strips of this and mail it in to us for development as soon as you can get it.
Another:
I am informed that you will find some very excellent examples of plantation homes [in Alabama]. Incidentally, most of them are in a sad state of decay. You will probably have an opportunity here to get some good erosion pictures.
We would then like to have you take the jump to Waycross, Ware and Brantley Counties, Georgia. In this vicinity you will find the Coastal Flatwood Project. Here you will find cut pine lands and turpentine workers. Get us some good 8 by 10 shots and also some good Leica shots of the turpentine workers.
By the way, I checked, it was an 8x10, not a 4x5 (as I mistakenly wrote) that he carried in Alabama in 36.