I love to donate blood! You are made to lay back with your feet up for a while (this never happens otherwise in real life), you are given free cookies & juice, you can (try to) get your family to do your heavy lifting for the rest of the day, and best of all -- you can save up to 3 lives with your donation!
I like to think about & pray for the folks who will receive my blood while I'm donating. I have the perfect blood type for a teacher or student, it's A+. My local feed store hosts the traveling Bloodmobile every 3 months and offers a free bag of animal feed (up to $15 value) for every donor. So I try to coordinate my donations with that. I hope the chickens appreciate what I do to feed them.
You cannot get a disease from donating blood, and instead could become healthier. They do tests on your blood, and also check your blood pressure & heart rate, and will tell you if there are indications that your health is at risk. This early detection could save your own life while you're saving other lives.
It's always worth the attempt, even if you think there's something that might prevent you from donating. Read your questionaire carefully, answer honestly, and the folks doing the collecting will let you know if you qualify or not.
Blood donors are life savers!