Unpaid blood donation!

I wonder if there are some disadvantages to giving an unpaid blood donation or if it is bad for our body?

I would define a 'donation' as free. Here in UK, no-one is paid to give blood, but they do it anyway because it is for the benefit of everyone.

Unless you are seriously ill, your body can replace 0.5 litre of blood in a very short time without any negative effects on your health.