I had the opportunity to consult with a course that had parallel (with the same playing distance) par 3s early on the first nine. It was designed specifically to improve the pace of play.
What this design actually did was make the pace of play worse - much worse!
Through all of my research, I have found that the single biggest factor that impacts the pace and flow of play, is overcrowding the golf course i.e. putting too many playing groups in too little real estate. Encouraging two groups to play alongside one another on parallel holes, totally erases any separation these groups ever had with one another, and as this course did, creates delays on the following holes along with a wait of three or four groups on the tee of the next par 3 hole.
This is just another example of how many of the so-called remedies for slow play are wrong, and why most of the cures for slow play are counterintuitive.