Maxx - you sure can. It's personal preference on where you place your projector. Some put it on a coffee table in front of their seating area, some in a tall bookcase or shelf in back of the room, some on the ceiling. For me, I have a very big room and want a relatively stable, permanent setup so ceiling mounting is my choice.
The benefit of mounting it on the ceiling is that once you get the image sized and orientated properly you won't have to do it again since generally speaking the pj won't move again.
The benefit of shelf or table placement is that it remains very portable and you can move it from room to room or even take it to a friend's house without much effort.
It's all up to you...