2000 Disco 2 Do I really need to turn off the cruise button every time?
 

The manual says in bold print to turn that button off when cruise is not needed.

Do I really need to turn it off and what am I risking if I leave it on or forget on occasion?

Lets say you were stalking 2 Rhinoceros. Whilst moving forward in low gear you strike a termite hill with your right tire. The live axle configuration of your front axle will make the Rover jump and possibly hop to the left. If you were not anticipating this movement, your hand may slip activating the cruise control. In this instance the rhinoceros may be alerted to your presence and the hunt is spoiled.

That being said--the computer isn't thinking any harder when the cruise is on or off.

Mine stays on 24/7. Like bikingteacher said, only turn it off if there is any chance you may accidentally engage it when you dont want it.

I don't have streets long enough for cruise control down here in the virgin islands

I haven't turned mine off since I purchased the Discovery years ago. The manual statement is CYA for someone who runs the Discovery through their garage door because they hit the wrong button.

My master cruise switch has been on for over 2 years.
And when I hunt rinhonosioussssss, I walk and use a .22, its more of a challenge that way.

Who "stalks" a rhino at over 35 mph which is where the cruise control will engage? That would be a chase and stealth goes out the window during a chase.

It won't hurt anything to leave it on. Worse that may happen is the indicator light in the switch will burn out. $3 from AB. Yes, they are incredibly expensive for what they are.