To those thinking rarehopping is tanaan exclusive, let me show some ways I have used realmhop to my advantage recently - some of these will be 'clever' or 'positive' some will not be.
Leveling experiments - this largely involved realmhopping and killing rares in vanilla zones. Also used it to get quest objectives more conveniently rather than waiting for spawns and to avoid high level players killing me.
Rare'camping' the 5 or so WoD mount rares outside tanaan. Took about 2 hours for all combined rotating through approx 35 servers.
Hopping to not wait for nalak spawns
Doing reputations like explorers in about an hour by realm hopping the chests.
Isle of Giants bone farm - rather than trying to get any tags on my servers I just grinded a couple groups serverhopping.
5k blackfang claws achievement/mount - once again rather than moving i just repeatedly killed the group by the felpool and then immediately hopped.
realmhopping to get spawns and also not count for daily progress at same time while doing the king of beasts? achievement or something
there are probably more... if i have an issue and feel realmhop will alleviate, I'll use it. I have the window on my UI so it's convenient.