Where 76 keys come in handy is when you make a 2nd split to the right...
Or when you play a lot of piano parts on your key..

The trade off, its a little heavier and bigger..
I can imagine especially the size being a negative for people owning smaller cars..

Personally i would not want to miss the extra 15 keys on any keyboard...
But will you miss them if you have been used to 61 keys all your life?