i use to do this when i was poor. Its an easy buck. My place paid 20 the 1st time in a week and 30 the 2nd. Later I found out ( from a personal friend that is a plasma "scientologist?" someone that works in the lab) that plasma is where you build antibodies, basically to keep your immune system healthy. You can deplenish them as you donate.
its true you regenerate plasma quickly but the antibodies dont replenish as quickly.
this is what i heard and inferred.
I got sick probably 2 months after donating ( everyday ) and was sick for 5 weeks. sucked balls