There are two advantages and one disadvantage (that I could think of) to adding it.
Advantages:
- Would make the use of heavy cavalry more tactical. Because you wouldn't want to let your heavy cavalry get tired without a good reason.
- Would help balance horse archers. They wouldn't be able to just keep running forever and pouring down arrows on the enemy.
Disadvantage:
- People don't seem to like the idea of stamina overall(?).
Advantages:
- Would make the use of heavy cavalry more tactical. Because you wouldn't want to let your heavy cavalry get tired without a good reason.
- Would help balance horse archers. They wouldn't be able to just keep running forever and pouring down arrows on the enemy.
Disadvantage:
- People don't seem to like the idea of stamina overall(?).