Practically never. At least not in the US. I used to work in downtown Atlanta, where there were panhandlers galore. How do you decide to give to ONE and not another one? I would rather give to an organization – food kitchen, shelter – than to an individual.
The other issue I have with giving to individuals is that I doubt they will take my money and do something worthwhile. More likely they will go into a liquor store or gamble it in 3-card-monty.
In any event, the answer is NO.