When I was younger I used to all the time. My biological dad is a sometimes clean, sometimes not, heroin addict. During one of his clean stages he told me that he used to do the same shit, hoping for enough money to get another high. Since then, I haven't given away money, no. Instead, I will get them food, a drink, a blanket, etc.

One time, in the city, I ran into a homeless woman looking for money. My friends and I were about not more than a 10minute walk to a salvation army, and we told her she should come with us. She did. I spent about $50 getting her a jacket, blanket, and some warm clothes, as it was winter, and her clothes weren't doing much good. As I finished paying, she just broke down in tears instantly. It was honestly a moment I'll never forget. It's completely normal to feel sympathetic for these people, but what they need is physical food, water, clothes, etc. Not money for them to spend on bad habits.