As far as I know, right now rank has only 2 effects. First, the higher your
rank, the more faction points you can store up at once. Being able to store
more is useful when you want to buy expensive faction perks, like those 9k+
ATSTs. The second benefit is that if you transfer faction to another
player, it costs you less faction to do the transfer.
Here's the table of ranks, showing how much faction you can store and the
cost to transfer, which I have copied from another post elsewhere on these
boards.
RANK = Points required to promoted rank = Amount of points you can hold at
current rank (10.1 x Amount of points spent to acheive that rank) = Ratio of
delegated transfered points (example)