The list, or manifest, is helpful to the purser when s/he makes out the list to ask each F class pax by name what they would like to eat...
The manifests are just a part of the paperwork handled for each flight. There's a lot more, from what I've seen. Very interesting stuff....
I will say, not ever having seen the document myself, that a couple of FA's this year thanked me for being a UA FF, even though I had not attained any status at that point. I'm sure they weren't flirting with me, so perhaps there's other information there. In any event, it was nice to hear.
Pat