It is a good effect, and can really add impact to a clip, but don't use it just cos you can, it becomes very tedious very quick like most effects and adds blur to your vid.

It is good for live action like motorcyle stunts, car stunts, crashes, slowing to freeze frame or if your remaking the matrix.

It tends to work best if camera is set to a slightly higher shutter speed as then the captured video has less motion blur to start with.