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

I did for years until I learned about toe in.  I have one pair of towers with no toe in and they sound good in a large open room.  I toe in the other speakers I have in smaller rooms with more surface reductions.  Adjusting speaker placement as needed and preferred is a fun part of this hobby in my experience.  

I have a pair of Snell Type A's. They are designed to go flat against the wall and face straight out. They rate in the top category for sound.

Try this, Toe in the speaker one click,1/8 of an inch at a time on both speakers at a time, stop and listen, and you will notice the center will get better without losing soundstage. It should be very noticeable. You will get a sharp center, without losing soundstage on the side. The speaker will disappear from your room.

The formal answer is that toe in affects tweeter rolloff, the width of the sweet spot, the treble to midrange balance and early reflections.  There's also the issue of some excellent tweeters may have resonances which completely vanish a little off axis.

Many speaker brands are designed to optimally perform with little or no toe-in.  I include:

• Magico
• Focal
• Revel

Magico and Revel in particular have great imaging across a wide listening area when placed with little toe-in and plenty of space to the sides and rear.

A little history may be helpful.  In the last 30 years or so tweeter manufacturing has come a long long way.  Cheap (< $50) tweeters often flat past 20 kHz, wide dispersion and low energy storage.  In the old days this was the realm of exotics, and if you wanted to hear everything you needed to point the speaker right at your head.

A related issue IMHO is the tweeter height.  Some speakers, like B&W, really should be listened to on mid-range height, not tweeter height.  So in general the best listening position for many speakers in the 21st century is with little toe in and perhaps significantly below the tweeter's laser like axis.

Harbeth  40.2,  backs against the wall and pointed straight ahead.These are a deep cabinet speaker and I just don't have room to pull out. I've always liked the sound from these speakers and haven't tried different arrangements except a little toe in. I find with no toe in the imaging is really good.