I am a fairly crap surfer, but I am reasonably competent on a SUP. I have never had the upper body strength to paddle for a wave, then have the strength left to get to my feet. On a SUP I can surf for hours on end without becoming exhausted.
I have a shortish SUP (8'11") because it weighs almost nothing and is easy to lift to and from the storage rack and fits inside my car without too much dicking around.
The only thing I miss out on with a short SUP is the super early takeoff you can get with a really long board.
Even with a relatively short SUP I can still drop into a wave as it is breaking and I am already on my feet and riding. When you consider a ride on a small wave, or a closeout beach break, can be as short as 10 seconds then the extra 2-3 seconds is a heap more surfing, and arguably in the best part of the wave.
On my SUP I can go and have good surfs on breaks that other people don't ride because the waves might be considered inferior. That's a bit of a joke because I am often out alone in perfect waves because I surf the alternate breaks.
Because I have had a heap more surfing on my SUP, my short board skills have improved and I can now have decent surfs on my 6'6".
As a crap surfer the novelty of being in the perfect position on a head high wave has never worn off. When I am in that position on my SUP it just feels so good and the SUP feels just as short and nimble as my short board.
I also get to play air guitar with my paddle and that is always fun.