I don't have a boat but I took a 3-day course RYA helmsman last summer in anticipation of buying one next year and as part of my "experience being in a boat before you buy one".
My thoughts echo much of what has already been said:-
You will learn much more than just driving including safety tips, some of which are not necessarily instinctive, at least they weren't to me......i.e. man overboard = turn off the engine first before trying to help them........I'd have chucked in all the lifebelts, ropes and good swimmers I could find before I'd have thought of turning off the engine!
I also found the instruction on rope handling, knots and mooring techniques really instructive.
It was great to have someone experienced to "lean on" particularly when locking and winding and I now feel confident in reversing and manoeuvring the boat through what I used to regard as tricky situations
Add in things like canal etiquette, the "Highway Code", daily boat checks, help in understanding (maybe beginning to understand) boat electrics, pumping out/Elsan, filling with water and diesel etc., etc. All things experienced boaters don't think twice about I'm sure but stuff which i'm glad to have had a shortened learning curve on.
Another thought, which I touched on above, is everyone says to "try before you buy". A live-on-board course is pretty much the same daily cost as hiring a boat anyway so if you're in "try" mode there's nothing to lose really.
Plus it's really good fun
I've held back from mentioning who I did the course with as I'm not sure the moderators would want me to name them? Like you, I'm a newbie to this forum but if you can work out how to message me I'd be glad to tell you who I did the course with as I'd recommend them all day long!