Classic Returning To DF, Cross Faction and Realms Questions

Came back to the game and noticed you can join groups for PVE content which are cross faction which is fantastic. Furthermore, you can mail across faction (at least for the same account) and overall it seems they have minimised the difference of being in differnt factions. Is there still anything noteworthy that is exclusive if you are on 1 faction or the other, I mainly want to know since half of my chars are horde and the other half are alliance but all my friends are Alliance. I'd like to know what I'll be limited from playing with my freinds who are alliance if I chose to level some of my horde chars.Also, what impact does Realms still have? What does the realm determine now? via /r/wow https://ift.tt/R27WA6K