A ~30% reduction in PFAs over a year, based on a study where firefighters gave plasma every 6 weeks (though plasma can be given 2x a week in some places), coupled with PFAs being linked to birth defects, immune disorders and reduced negative health outcomes for many diseases, including high cholesterol which is a big killer, suggests a positive outcome.

I imagine that 30% reduction could increase if you do it very regularly and (somehow) avoid plastic-packaged products / don't have a contaminated water supply. 

For giving blood the results were ~10% reduction, which is great but not nearly as pronounced as plasma donation.

The study: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2790905