I chartered last summer a Hanse 495 which I had to get out of, and into, its slip at Granville Island, Vancouver, BC. VERY tight in there. Also, going in and out of a slip at Coal Harbour in Vancouver. The marina fairways in Vancouver/BC are not "generous." Thus, when you're backing or going forward into a slip in an area with little room to turn the boat using the screw/rudder only, a thruster is a welcomed addition.
It's also useful when positioning for the anchor drop and you wish to go slow (read: a lot of rocks and other boats around) but the bow begins to fall off b/f you're ready. And, as probably no one would like to admit having much experience with, it might help you some day get off a sand bar, mud mound, or other shoal. However, I doubt that I would ever pay to install one on a boat of much less length than the 495.