We use this approach in our company, but only for the difficult tasks or when you're unsure about something someone else has worked on already which I believe works very well. It saves you getting stuck in a rut and being able to bounce ideas off people where necessary while still being able to work independently for most simple tasks.
I also believe it is more beneficial than a code review, which is something else we do where I work. It is often difficult to know fully what's going on when doing a code review without providing significant context, at which point you don't always have the time to think about all the in's and out's. Pair programming gives you that context from the start and allows you to spend more time thinking about edge cases that may or may not cause problems.
