[j32fun]

Most often it's to try and help the other person become a better programmer. I've found that people who have little desire to improve end up sitting there regardless.

The underlying desire to do it, of course, is to give the programmer (the one who we're investing in to improve) a chance to improve. It feels, however, like a wasted effort.

[robinanil]

I see, often the person who has little desire to improve needs to be handled differently.

There are various ways to handle low performance, including talking to the person, finding out the reason behind the low performance. Most often it is caused by external factors.

Pair programming or any such coaching tool IMO are effective only after you dig deep into the reason behind low performance. Once the individual is ready to improve, that is when you can employ pair programming.