When we got the new boat we spent a bit of time sailing onto the mooring with the engine available if we needed it, and we still often sail into the mooring to make sure we keep up our boat handling skills. Given the very high number of boats that end up with a rope around the prop when they try to recover a MOB, it seems that being able to sail up to a mooring or MOB without the donk can be an important skill.
One of my more embarrassing moments (and there's been lots of them) was not running out of fuel when trying to get back to the mooring, but realising I'd left the keys in the dinghy. We were down-tide, with no wind. Luckily there was an oar or paddle on board so I got to spend a desperate half hour or so padding a 28'er as hard as I could so we could get up the river and onto the mooring before the ebbing tide got stronger and pushed us and our guest down harbour for the night!