It almost always turns out to be a pain in the neck beyond all expectation, and the person you're doing it for isn't even grateful (well, not grateful enough anyway) because they have presented it as a trivial task. Whereas things that people ask of you as a favour and are grateful for afterwards often turn out to be a lot less effort than they think they are asking for, and even if it is a lot of effort at least I am aware when I agree to it that it will be difficult and/or time consuming and they are grateful.
I feel better for venting.
My DM just asked me to do a trivial thing that has turned into a 30 minute struggle and required several messages back and forth between me and her because she didn't give me the relevant information.