I do as often as I can, which is every 4 months because I donate double red cells. I am O negative so my red cells are extremely useful in emergencies and it is something I can do to help other people. Donating doubles they give you your plasma plus some saline back so you end up with the same volume of fluid. Because of this, I feel perfectly fine afterwards. I am currently at almost 7 gallons donated.
I always say I want mine to read “He died the way he lived” and then say how I died. The less sense it makes the better.