I never gave it thought when I got my dog. I put the food down and if I need to add something I picked up the bowl even if he was not finished yet
and put it back down with something tasty in it. I don't have any aggressive behavior. One time with my other dog when he was a pup I took him to obedience school, they told me to feed his kibble to him a hand full at a time till it was gone for a couple of days. I thought it was a strange method. Thankfully he was not aggressive with his food either.