Flying Mount Takeoff Option

[ItMe]

I'm going to guess that the second option performs a check that allows you to fly while already in the air from jumping, while the first option can only initiate flight when initially entering the air on a mount.

The second option also lets you attain flight if you're already in the air. It's like toramorigan said, the game just hasn't registered they're on a mount yet if they're slide casting off a ledge.

The difference between the options is that one replaces the jump button with taking off, and the other maintains the jump function and you take off by jumping again in the air. The first setting doesn't prevent you from flying at any time you nornally could or change takeoff rules beyond simply replacing the jump function.