I bought an Infinity at the advice of the salesperson "no one buys the standard anymore. Everyone loves diving this". I was new and gullible.
Slowly I removed all the special little peices, for various reasons. The cinch was the last to go. I kinda liked it even though I didn't use it very often.
When changing to different tank and weight set-ups while traveling, I sometimes wanted to slightly vary the position of the tanks on my back to address trim issues due to a varying center of gravity. Also, when changing exposure protection, small adjustments sometimes made for better fit.
I agree that adjusting the harness on a backplate is not a real time consuming thing, but with the cinch a couple of times I adjusted it while wearing it in the water. Easy with a cinch; just unbuckle the waist buckle and pull.
As I got more into a technical flavored setup, I slowly floated to the simpler solutions. Having the D-ring mounted right to the waist strap was the reason that I finally took off the cinch. There is a D ring not on the weight pocket that can be used with the cinch, but my instructor was violently anti-gimmick, and I realized that at this point I did not really use the cinch. Since I removed it I haven't missed it.
I think that I enjoyed it during my training wheels period, but now that I am more comfortable with my gear it makes no difference.
If you would be changing exposure protection alot, however, it might be nice. My change of exposure protection is mostly seasonal, so its not so often.
I don't recall it ever changing itself by accident, though.
