Do I delegate?

I've done a much better job of delegating in the last year because I know what can be delegated and I know what those tasks entail. But I was thinking about delegation today and I wonder...Do I delegate or do I let people volunteer to do things for me? Is there a difference?

Last night, my Admin. Asst. said she would come in and set up the 8am focus group refreshments. Today, The Buildings and Ground Supervisor told me he'd set up the digital TV room for me. What my AA did was well outside her regularly scheduled hours, so I didn't ask her to do it. What the Super did was within his duties, but I hadn't given him the info he needed for room set up. I had planned on arranging it myself after the focus group was over. Hmmm... So do I take on too much myself? Is it all situational or is it habitual and would happen no matter what? I have to be honest. I would do it no matter what. After all, the program was essentially hosted by me, not something I really have time to do. Time to reevaluate delegation so as to be brutally honest with myself. Soft white underbelly, her I come!