The experience of pretty much every cruiser that I've known personally, as well as my on, is:
If you use it often, like every day or two, it is TOTALLY unnecessary. If you only use it every two weeks, sure, it would be a good idea.
Also... Carry a small twisted SS wire with you. The corrosion
inside eventually comes out in chunks and sometimes blocks the piss stream. (in older motors) The older the motor
(like10 years), the more often it happens. Just keep an eagle eye on the water
flow, and if it stops or turns to a spray pattern, stick the wire an inch in the nozzle, and wiggle it around, while it is running. I have done this a hundred times, and it hasn't failed yet.
Yes, that means that the inside of the motor
is corroding out... V E R Y slowly. Usually OB motors don't "wear" out, they "corrode" out. Still, 20 years is quite possible!
In spite of this being the case, the outside is corroding out too, and rinsing the inside daily, is just not practical while cruising, (unless you are a weekend cruiser). Then it is worthwhile, because you will be back at the dock
, with a hose & lots of water.