If you tap a mob by Wanding/DoTing/ or using direct dmg attacks your pet can finish it off and you will get experience, if you are in a group with a high level that's running you through an instance you can sit inside the instance portal and gain all the exp from kills as well as loot. And btw if your in an area where you can get experience I highly doubt you can go eat with your pet on aggressive, he will die quickly to yellow mobs or last a little longer against green mobs, like 2-3 yellow level mobs, 4-5 green level mobs, then once he dies the mob comes after you and you die.