I have used the 3.5 hp Mercury as a dinghy motor and "Kicker" for a C Dory 22. I have also used (and still use) the Suzuki 2.5 hp p 4 stroke outboard as a kicker on a 22 (and currenty on my 18' Caracal Cat). I also used it on the Tom Cat and CDory 25. These smaller kickers will give stearage way, and will push the boat at 3 to 4 mph.
I once had an emergency, where I had lost the transmission on a 62', 65,000 lb Pilot house ketch motor sailor. I used a 4. 5 hp on a dinghy to obtain stearage way, a speed of about 2.5 mph and kept the boat safely on course unitil I could launch a 13' inflatable with 25 hp (which pushed the boat at 5 mph--got sail made and 7 mph. My dad's 26' sailboat, with a hull very simiar to a C Dory 25 was pushed for many years by a 5 hp outboard, and it would go 5 to 6 mph.
The small motors cannot push you against heavy winds and seas, but are enough to get the boat out of a jam in over 90% of the time. I have never relied on "commercial assistance", but always hoped to be able to "self rescue" in case of "emergency".
Also other than running out of fuel, (preventable), and fuel line relataed issues, catastrophic failure of modern outboards which are well maintained are extremely rare, but will occur.