The short intra-set rests keep bar speed and technique high at heavy loads, so a lifter gets more quality reps at 85 to 90% than straight sets allow. Example: 4 clusters of 2 + 2 + 1 at 87%, 15 to 20 seconds inside the cluster, three minutes between clusters.
It is a strength and power tool, not a hypertrophy one, and it needs a rack and a timer.
Total reps at the given percentage is the number to progress.