My general rule of thumb is:

If you can move the part to the tool and control it easily, use a bench tool. (Either a bench grinder or disc sander)
If you can't move the part to the tool or control it easily, use a hand tool. (angle grinder, Dremel, etc.)

At work, we use a disc sander more than anything for cleaning up and light shaping. It works well and is easy to get a clean square edge. Bench grinders are used more for sharpening tools than anything, but the occasional bolt modification or polishing job is done on it too.

The biggest problem that I have with bench grinders is that they typically don't come with decent stones. These can be as much or more than the grinder was on its own.