I'm fairly new to php and only do it as a hobby, so quite often I'm on the recieving end of this, though not so much anymore.
Anyways, I find that helping other people can be quite rewarding and in many cases actually benefits me as well as the person I'm helping. In many cases I find solving someone elses problem can be a win-win scenario. For the receiver's side of it, they are able to achieve an effective code to run their ideas. In return for this you get to see this person's ideas and may even implement them in your own work.
If the person you're helping has a really good idea but just can't express it in code, I think their idea will be much more valuable to you (someone that really understands the code) than it will be to the person you're helping.
~and then there's always those standard questions that always seem to come up and do absolutely nothing for you