When you give a presentation, you will usually be standing in front of your slides, facing the audience. This is the standard setup for lecture rooms and there's simply no other way for you to do it, given the layout of the room.
Things are different with your typical meeting room, especially small ones. They are often equipped with a table in the middle of the room, around which the audience is assembling. The slides are then projected against one of the walls and often there's not a lot of room between the table and the wall for the speaker to stand in. I've seen such setups in meeting rooms at companies but also for user group meet-ups.
