Who positions their speakers straight ahead (zero tow in) and why.

It’s entirely an alchemy dependent on the OEM speaker brand influences in constant tension with the dimensions/design/ resulting warts of the listening room.

There is no “one-size-fits-all” general rule to follow because of varying brand speaker designs and performance capabilities. For example, the dispersion of a ribbon tweeter vs. A soft dome tweeter, vs. Concentric centred with a woofer design may all be different. Follow your OEM speaker manual for first guidance.

For the bespoke listening room factors portion in the equation, there are significant points of first reflection that are complemented with secondary ones, all three of which need to be identified and tamed if necessary.

TAKEAWAY:

There is no substitute for hands-on experimentation..

I’m with @akg_ca and others here. There’s no correct answer for every situation. I use a lot of toe-in with my current room, which is played long ways using horn speakers. One issue I just experimented with addressing is opposite side reflections, as shown by line "B" in @akg_ca ’s drawing. My side walls are about 10 feet from my listening position, so there’s an extra 20 foot path length to create a decent delay. But, I wondered what would happen if I used angled panels to redirect that opposite wall bounce away from my listening position. The result is very interesting, and overall quite good in terms of imaging enhancement. So even when fairly significantly delayed, cross reflections can be detrimental to imaging, which could be a reason someone might not want to toe in their speakers in some rooms.

One thing that I found enlightening from this experiment is that my old idea of only worrying about reflections that are inside the "image shift" window is not adequate. There’s more to imaging than just the left to right positioning of items in the sound field. By controlling that opposite side reflection that’s outside the image shift time window, according to the chart I’m looking at, a lot more dimensionality and immersive effect has been preserved. On some electronic music it’s pretty much a full surround experience with just two channels.

I remember when I for Tritons, Sandy Gross recommended having them as far apart as possible and toed in pretty severely. I don't even recall if I ever tried it.

I've been experimenting with  speaker position including toe in. I was listening to a David Crosby cut off "if I could only remember my name", and heard wonderful instrument placement, artificial or otherwise. I went back to what had been my original listening position that had provided a great sound stage earlier but found when I listened to the same song,  what was a fairly precise location had totally evaporated and it was merely a piano coming from somewhere. I have tape on the floor so I put it back where it was. The total distance that I rotated the speaker was less than half an inch.

It depends on a few things, but I have found that speaker placement is mostly speaker dependent. I had a pair of KEF Reference 5 speakers that sounded their best when almost facing straight forward and 3’-4’ from the front wall. The Sonus Farber speakers I have now sound best when aimed at my shoulders and 3’ from the front wall.