Ok, this post got a little long, but it was fun to write
tl;dr at the bottom.
Setup: I am only 12 months into my sailing career.
Punchline: By my experience, I'm prepared to unequivocally renounce the use of engines on daysailors. And on the internet too!
Allow me to state my case:
After taking the requisite ASA courses (through 104) at a boat club in San Francisco, just behind the ballpark, I started renting club boats. These were Santana 22's, a wonderful little dayboat that can ghost in wisps and handle strong blows. At the club, they all came with 5hp yamahas on the back, and we were only taught to motor back to the dock. So, when the outboard died on my 3rd charter with a 10kt wind blowing out the entrance to the marina, I almost didn't make it back. I got caught against the breaker wall and had to fend the boat off before finally getting a tow. It was horrible.
I left the club and tried a 6 month 1/4th partnership (one weekend a month for $50/mo) on a 1965 27' Cheoy Lee P.O.S. With 30yo sails, no boom vang, a temporary outhaul, and a new skipper, she barely made sail. I foolishly agreed to take a novice crew to Angel Island, and was too worried to put up sails when 25kt winds picked up. The inboard diesel engine did nothing but billow smoke as we crawled home against the current. It took us 5 hours to get back. It was horrible.
Still in love with sailing and tired of getting what I paid for, 4 month ago I bought my own boat, a 1975 Dufour 24. Every weekend and many holidays since then I've spent at least some time at the boat.
The first month was spent working on the inboard diesel engine (yes, on a 24'er) a raw water cooled volvo md6a/7 hybrid. With the help of the previous owner once removed, I got it running, but on my first shakedown, the engine started to overheat as soon as I left the breakers. Now I am not an experienced sailor, and I was out solo, but I also had a plan expecting the engine might fail as so many others have. I ended up sailing back to my slip for the first time. It was...wonderful!
The 2nd month was spent trying everything short of surgery to solve the overheating problem. Fluid change, Salt Away, impeller. I would do some work, then go out with friends family on calm days (It's been an incredible winter for light air sailing in SF. Sorry rest of the country...), using the engine sparingly. This resulted in several more dock under sail attempts, a few rocky, but all successful.
After a bolt on the exhaust manifold broke in it's housing, I was done wasting sailing days covered in grease. The third month of boat ownership was spent sailing without an engine, and I've never enjoyed sailing more, sailed more often, or been more dedicated to the craft of seamanship. For the first time, sailing is living up to it's romance.
1) Engines break, and if they don't break often it's because you aren't sailing enough.
2) When they break, you are not in trouble because you don't have a motor, you're in trouble because you don't know what to do. Trying to prevent the second problem is safer than trying to prevent the first.
Caveat - I'm only talking about boats under 5000lbs, because that's all I know, and more than that it's a momentum problem.