Sailing in gear or in neutral?
This has come up many times before and the results came down to keeping it in reverse while sailing!
Less wear on the cutless bearing.
Less wear on the transmission.
And if you have a folding or three blade prop. Put marks on your shaft for alignment for better performance.
There were no advantages, to letting the prop run free, that I could find!
Some run a generator off their prop. so that''s going to be higher maintenance.
I don''t like the noise!............................._/)