It makes sense that the mouth is located near the eyes (and if existent, the nose) so you can see (and smell) what you eat and directly rule out that it's poisonous or otherwise unhealthy. It also makes you more efficient at getting the food before someone else does or before the prey swims/runs/flies away. Imagine if your eyes and nose were located on your ass. You see something that you know is edible, grab it and raise it to your mouth, out of your side. No a poisonous insect sits down on the food you're about to eat, but you have no idea and when you eat it and notice it's already too late.