And those things make far more difference in the long run. I never give to beggars aside from occasionally buying a "big issue". By my understanding (which I'll admit is almost entirely based on second-/third-/more-hand information and a chunk of cynicism) you can make far far more difference overall by donating to relevant charities and other such groups if you want to help financially, or (as you say) donating your time and effort to those groups by other means.

[] the cynicism part comes from things like the woman who for three years now has been trying to get together the bus fair to Hull, or some years ago seeing someone who earlier had been sat on a corner begging get into a car that appeared to be his and drive away