"Free" is usually a bad deal for both the client and the consultant. The client is automatically in last place on the consultant's list of priorities, regardless of how important his work is. The consultant has established a $0 price floor for her work, making it that much less likely that she'll ever get a good project from the client.
If you do stuff for free --- and we do --- make sure it's different stuff than what you charge for. We are, for instance, happy to give free advice, or to chat on the phone with you about problems. We are not going to be happy to take a little time testing your app.
This isn't just me pontificating. More often than not, when I've tried to help people out with free project work, things have gone badly with the project itself.
