What’s the benefit of placing speakers like this? (diagonally at the corner)

Possibly of interest: room diagramming tool for measuring where things might go. https://sourceforge.net/projects/sweethome3d/

For those dismayed by the disjointed "look" of this setup, you could put an entertainment center type shelving unit diagonally in the corner.  It would create a false wall at the 45 deg angle, but would be symmetrical with the speakers.  Sonically it would not obstruct low frequencies, and it would diffuse upper frequencies.  ALSO... since the corner behind the shelves would be unusable dead space, you could put a large corner bass trap there.  This would be a great solution for a large room, where you wouldn't mind losing a few square feet to the corner.  

https://systems.audiogon.com/systems/3798

In my space, the diagonal allows for good symmetry when it comes to space from walls and listening chair distance. This allows for good soundstage balance (a very important factor for me). And the space that would be needed to set the room up asymmetrically in the room (far enough away from the side walls with a large open space on the other side) would be significantly more than a corner set up. 

I haven’t had my system set up in a rectangular room in years and I can’t remember the difference.  But here seems to be minimal smearing from side walls in my set up. I found that there was a much larger amount of interference from the speakers sitting too close together rather than too close to the side or front walls. 

So I suppose my sense of the benefit would be physical symmetry and use of space.