That way you can just jump into whatever raid from dungeon heroics. It'll fix stat inflation. The previous raids won't be obsolete for the rest of the expansion and you can't faceroll over previous content to get cheevs until next expansion.
"I was a normal baby for 30 seconds, then ninjas stole my mamma" - Deadpool
And YOU will slaughter them, because you'll have to take them from their dead and cold hands.
OP: woohooo and everything for that new, looks awesome. Personally i'm not leveling a single alt before they make it easier, because 85-90 with my main was the most boring and frustrating experience in my WoW career. Frustrating, because my guildies were already running heroics, and i felt like i was left behind, stuck at level 88.