I would like to know, what is the advantage of practicing PVP on other servers?
You start everything from scratch, leveling the character, setting up gear with difficulties, because that's the fun of the game.
When entering BG, you are faced with Blackrock players, with ready sets without any difficulty.
Servers for fun, should be just between each other, and join only common servers in BG.
I don't understand the logic.
I think Blackrock is a cool server by itself but, crossrealm BGS with Icecrown/Lordaeron should not be a thing. Personally, I think all crossrealm BGS should be turned off. I personally play on Icecrown, but for players on Lordaeron BGS are not balanced either since on Icecrown you can pay for gear and then theirs Blackrock. This should go for arenas as well, same problem.
Usually servers have crossrealm because ques are slow and take a while to pop due to population but, i'm sure all 3 servers have more than enough population for pretty fast ques, so i don't see why they added crossrealm in the first place but just my opinion.