Lots of people seem to have been lucky without a kicker, but I wouldn't go anywhere without one (unless the boat is small enough to be rowed with oars), and have used them to get home at least twice.
Once was on my 16' arima, when my brand-new 90 hp E-tec decided to just turn itself off and not run, just as we were heading out of the marina. Used the kicker to get the short distance back to the dock, but without it we would have surely been on the rocky breakwater within a couple of minutes.
The other time was on a 21' boat with an I/O mercruiser that was perfectly maintained and in like-new condition. I had just bought the boat and we had gone out a couple of times without a kicker but that made me super uneasy. So I installed a Yamaha T9.9, and on the very first trip out with the new kicker, the main engine died (ignition coil) somewhere near Oak Harbor and we got to "break-in" the new kicker by motoring about 5 hours back to Everett. It was slow, but a nice day and so we enjoyed every minute of it.
In the second case, without a kicker, we probably could have called and gotten a tow but that would have been expensive (and embarrassing!), but the first case happened so close to shore that we would have been at risk of causing serious damage to the boat without a kicker to get us off the rocks immediately.
-Mike