Hopefully, your listening room is not square. A square room with all dimensions being equal is a recipe for the worst room modes possible.
Fortunately, most of our rooms where we hope to set up a stereo system are not 8'x8'x8'. (If this happens to be your situation, consider a near-field listening setup instead).
For the most part, our rooms are rectangles where the challenges are fewer but decisions still need to be made.
One of the most common questions I get is whether to place the speakers on the long wall or the short wall. Fire into the length of the room and deal with the speakers being too close to the side walls or deal with your seating position so close to the rear wall?
Of course, the easy answer is to try it both ways but that's a royal pain in the keester.
My best advice is to almost always point the speakers so they fire down the longest dimension in the room.
It's been my experience that it's easier to tame the sidewall problems with diffusers and absorbers than it is to limit one's self to dealing with the lack of space behind the listener and the speaker.
When it comes to rectangles, the benefits of space behind you and the speakers outweigh the problems of a narrow room.
