I have struggled to reconcile what I think I'm seeing in slow-mo videos/clips of pros and what I believe is good advice on hip movement.
In the vast majority of pro clips, down swing with club shaft parallel to target line, the trail elbow is at the trail hip or a hair in front. Coming into impact, the hips are open. Various Ben Hogan clips show this well. A favorite is Couples - by the time he reaches impact, his hips are very open.
On the other hand, I have read the posting here by Matt and VJ where they caution against hip spinning, use of the dowel-in-the-belt loops to stop the spinning, etc. I have seen Tom Tomasello's video on this site where he clearly shows keeping the trail hip back and swinging through and past the restrained hips (i.e. keeping them closed coming into impact).
I can't believe 'open' or 'closed' hips - as a swing thought - into impact are both correct. What seems to work well for me is the Tomasello approach of keeping the hips closed and driving the trail elbow past the hips which then open up somewhat coming into impact - but the hips are 'following' the trail elbow, not leading or connected ala Hogan.
I've tried to decipher this and remain confused because (1) excellent pro level swings certainly appear as trail elbow riding the trail hip into impact with hips quite open at impact (2) Tomasello and others advise keeping the hips closed and swing 'past' them.