I'm a 3 and out kind of person. I've had about 5 jobs in 15 years. The last 4 were all 3 year stints.

I just finished year 3 in my current position, but I'm not actively looking, so this might be a new record for me.

Useful? Well, sure. All experience is useful. There are lots of reasons for changing jobs. Money is one, but just 'doing something else' is another. A danger of development is that you often get sucked into things you don't want to do after a while. You become the 'expert' on the app you developed, so that means you go into production support. Or into managing it because it has grown beyond a couple of people to a larger team. If that isn't what you enjoy, you may want to switch jobs.

I've lucked out. I've never regretted a job change.

Edit: Fixed typo pointed out by ysth.