Why make reservations?

So I got a call from the blood bank last Friday asking if I could come in and donate. Really! Kind of surprising but after the phone screening I was told I could donate. So I made an appointment/reservation for 7 PM. Figured that would be a good time of day, relatively low wait. There are a few flaws in that plan.

1. I still had to wait 30 minutes.
2. I had to fill out the screening form again
3. I had not eaten dinner yet. I would have eaten if I had known it was important.
4. The stress of the day made my Blood Pressure a little high.

So I am still trying to pay it forward.