When to use high gear on 570

Picked up our new Sportsman 570 today. Never owned one before. Brand new, EFI, base model for $5300 plus tax and title.

So the dealer is telling me to keep it in low gear unless I am consistetnly over 25mph such as on a trail. Does this sound right? The manual says anything ounder 7mph to keep in low gear. Whats the popular wisdom on this?