It's known that squeezing the abs is one of the most important rule of (to my knowledge) all workout exercises, especially with weights
The reason of this is the ability of ths abs to stabilize the back preventing it from overarching (anterior pelvic tilt) to get momentum and make the exercise easier (let's think at pull-ups, overhead press etc).
This is very useful because in such exercises there is high risk of anterior pelvic tilt. I can understand the importance of abs in such situations since they their shortening may tilt the pelvi backwards and counteract the anterior pelvic tilt. For the same reason, in many exercises it's advised to squeeze the glutes.
What I don't understand is why squeezing the abs is a must even in all exercises where there is high risk of posterior pelvic tilt. I'm thinking for instance at squat (butt wink), deadlift and barbell roa. In such exercises I find it more difficult not to go in posterior pelvic tilt. Why should abs shortening help me?