One of my rogues was alchemy from TBC all the way through MOP. Caught a lot of garbage for it... But as everyone knows I never care what anyone has to say when it comes to playing my toons.
I believe the potion itself is +8 agility which actually works out to be +13 agility if I'm correct.
With sub rogues already having 54% crit or so it would make more sense to roll alchemy and pot it up.
Kind of been saying / doing this for years but some people just like the constant crit %. Farm it and you're done.
Then again most rogues are assassination these days.