It's not a bad thing to do in the right circumstances, provided you put limits on it as you don't want to be taken advantage of. You might innocently help someone with something which doesn't take too much of your time but then you'll sometimes end up getting spammed with other questions and requests and it can get draining if you don't know when to say no. I've been there before, far too many times. However it can also be good to help build up a reputation, as it'll lead to more prospects for paid work etc so you could consider it as marketing.