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

Reference 3a decapo i has a Deapollito design where the tweeters in this two way design are offset to the left and right of the woofer.This means that time allign correction/ image is best when straight ahead.I tried toeing in slightly and it collapsed the width of the image so I keep them straight on as recommended.

I have Vandersteen 5A's......I have them 1/2 way between straight on and facing me when listening.   I experimented years ago ....I presume that my final setup is correct....the speakers are way too heavy to move.

To many variables to consider on this subject.  Your ears must be the judge.  Sometimes, if your loudspeakers are too far apart - some small toe-in will help bring the center image into focus. This is a simple - no cost variable that we all face with box loudspeakers.

I have a pair of vintage Polk SDA 1C's, and I position them with zero toe-in because the manual recommends it. I think it's also proper given the interconnect cable for the extra stereo spread feature.

+1 @Locknow

+1 @Atmasphere

Equilateral triangle concept is great, however try this ratio:  distance between tweeters 1.2 times the distance from each tweeter to the ear in listening position.  I love big soundstage and getting the speakers as wide as possible (certain designs I.e. D’Appolito like my big Duntech Sovereigns lend themselves even better to this however I’ve found it fairly replicable across different designs).  
 

Ralph’s point about sidewall reflections also an excellent contribution- coming from a guy that has forgotten more about audio then most of us will ever learn :-)

Experimentation is key and often that’s the fun part!