With a single sub in a corner, the low freq. response will most often vary greatly from seat to seat. Sure, you could equalize for your money seat to flatten it out but chances are, you'd make another seat worse than it was before EQing. I found out this cold fact in my own room. When I first added PEQ to smooth the "best seat", it made others absolutely uncomfortable.
Your subwoofer/s should be placed to provide the most similar response to all of your seats - not always the flatest, but the most similar among them. This way, when you add your PEQ, every seat benefits.
The benefit of using more than one sub, other than increasing headroom, is that you can place a "virtual sub" in a location where you wouldn't/couldn't physically place one. When using two subs, they behave very much like a single sub located between the two.
Depending on your seating locations, and the width of your room, there will be a best location for a sub to be in regards to left and right to make more than just one seat in a row for example, the most similar in response.
With a sub in each front corner, using their individual volume levels you can shift the location of the virtual sub left and right to the best spot in relation to your room's width modes. If your design confines them to the front wall though, your still stuck with length mode issues to deal with.