Naruto Shippuden Episode 31

[Yukimura]

I think what the most practical aspect of the ability the turn off an eye techniques is surprise. An enemy can look at a person and easily identify them as a byakugan user by their lack of pupils even if they aren't actively using the technique. For sharingan users however, their inactive eyes look just like people with no doujutsu ability at all so you wouldn't be able to tell if someone had the sharingan or not unless they were using it.

This is a benefit since you could lure over confident ninja into engaging you in a fight and then spring sharingan on them, see through their technique, and kick their ass. For the byakugan if the enemy saw it they might recognize it and be inclined to just run like hell and making it that much more difficult (or at least more time consuming) for a user to kill them.

@Abdula there have only been two eye techniques revealed so it doesn't make much sense to say sharingan seems to be the only one you can turn off, until we see a third both are equally likely to be the 'different' one.