I gave some food to a guy once, he and his dog sit on a corner every day rain or shine, well, he took the food but he looked at me like I was crazy when I gave it to him. I'm sure he fed it to his dog, which is fine.
DBF was approached by someone once asking for money, DBF said to the guy "I bet you're better paid than I am" the guy actually said "you're probably right, I can help you get started if you want to sit on a street corner and work your own hours." DBF was not impressed. Needless to say that guy got no money!
As for me giving it, sometimes I do, depends on the situation, but it's never very much, just a handful of change usually, I don't carry much cash around with me.