Why do people do this?

Perhaps they don't have coverage, and can't afford to visit the doctor unless it's for something they know is serious.

Or they *are* planning on going to the doctor, but have to wait a couple days for their appointment so are seeing if anyone can give them an idea of what is wrong in the meantime. I've asked questions myself for that reason. I live on an island, so for me to get to my family doctor it's a 3 hour trip each way, and I have to make the appointment a week in advance.

Many can hardly afford to see a doctor for every ailment. So they look for input here before making that decision.

Of course, one must take answers here with a grain of salt, even Yahoo! implies that in their disclaimer. "Yahoo! Answers is provided for informational purposes only, and is not a substitute for professional medical advice, examination, diagnosis or treatment."

And there is always a possibility of getting informed answers here. For example a very close friend of mine is a doctor, and I sometimes answer medical questions with her help.