Are there any disadvantages to eating corpses?

If you plan on walking around in power armor you might have a problem since you can't eat people while in power armor. So you would have to exit the power armor to eat and then reenter which can get very tedious.

As for companions, you can tell them to walk away so that you may enjoy your meal in secret and then go fetch them when you're done. In addition to dogmeat not caring that you are a cannibal you can also bring Hancock who also neutral, or even better bring Strong. Strong actually LIKES that you eat corpses:)

If you play in survival mode in fallout 4, and choose to eat a corpse, you will get "dark cravings" and normal food will no longer satisfy you, you will have to eat more corpses in order to alleviate your hunger.