Cons: more particles in wort but easily remedied by allowing more time to clear before transferring to fermenter. Can't do very high gravity beers. Messy- not a good option for the kitchen stove.
Just to touch on some of those cons:
Even if you get more particles in your fermenter it will clear just fine, IME. You can still do high gravity beers if you are OK with brewing a smaller batch.
The messy part can be avoided if you don't start drinking until after you pull your bag
But seriously, I just quickly swing my bag into an empty bucket on the floor then deal with the grains later. There's no real mess involved there.