I have myself tried it, even though my subs were asymmetrically placed in my room, and it fixed a huge null and the booming I had in certain section of my room.
Tried it, and kept it.
Did you measure it, or do it by ear? And did you measure the effect at other frequencies and listening positions? Do you have before and after measurements you could share?
Obviously, you can cancel a wave at one location and frequency with an inverted wave of equal intensity. But two subs in a room are going to have a lot more interactions than one frequency at one location (unless, as I mentioned before, they are placed and calibrated with the precision of something like a double-bass array which is designed for full cancellation of
all bass frequencies after the initial wave).
This being the REW forum, I would suggest there's a better way to make sure the phase on your subs is set correctly in a multi-sub setup. I've attached some examples from when I recently set up an SVS SB-2000 and HSU VTF5-MK3 (as part of a four-sub system) I time delayed the HSU to match the SVS, and you can see phase graph and impulse response to showing how things look at the main listening position.
The red trace is the SVS.
The blue trace is the HSU with 180° shift.
The green trace is the HSU with 0° shift.
I've unwrapped the phase on the phase graph, and you can see which one is most in phase with the SVS.
On the impulse response, you can see which one is aligned with the SVS.
This is the first time I tried this with REW, so obviously someone can correct me if I did it wrong or am drawing the wrong conclusions. But it seems pretty clear to me.
Certainly, there are nulls and variances across the listening area. But even if shifting the HSU 180° helped with a peak or null, do you see how it would cause other problems?
Solve peaks and nulls by focusing on placement, EQ, and additional subs. Use phase to make sure all the speakers are pressurizing the room at the same time.