Perpetual for sure makes a difference and not just for number of harvests. I run perpetual in my 3x3, and if things are properly timed I can more efficiently use the space. As a mature plant is harvested a much smaller plant takes its place, leaving more room for the others that are finishing.
Even though there are always 4 plants, they don't each get 25% of the space all the time. A newly flipped plant doesn't need that room, but the finisher will use it. I may not have room for 4 plants at a time, each with 4-6 dry OZs of bud, but I can perpetually harvest that with proper timing.
I hope I was able to explain this in a way that makes sense.
Maybe a photo will help. I couldn't fit four of the plant on the left in there(it's got about 3 weeks to go here), but I can pull one that size from that tent every 3 weeks or so with proper planning.