Alan gave a nice description. Initially when you are improving your technique the focus should be on improving your efficiency by traveling further with each stroke. as your form continues to improve you reach diminishing returns on trying to lower your stroke count.
At this point, most TI swimmers are swimming long strokes with slow turnover. At this point, increasing turnover rate while still maintaining long strokes will allow you to gradually add speed back into your swimming while still keeping form intact.
I start people by having them do some TI focused warmup swimming, trying to streamline & lengthen their stroke. Then we do a stroke count and swim a few 25s while slowing down the recovery arm so taht there is more and more glide in each stroke. Soon they will reach a point where there is so much glide they are drilling and not swimming. At this point, gradually increase the rate of teh recovery arm while keeping the stroking arm essentially the same.
With practice, you can add exactly one stroke with each 25 repetition. Gradually increase the rate of stroke recovery and watch stroke count gradually climb. YOu should be able to hit a target number of strokes while maintaining good form by adjusting the rate of recovery and possibly the timing of your arms...(ie when does the stroking arm/body rotation start as compared to the location of the recovering arm?)
In this way you are teaching your nervous system how to modulate your effort in a controlled fashion so that YOU CHOOSE how fast you want to swim, and can swim that speed with deliberate intent.
Terry uses this sort of strategy in training and planning for OW race strategy as he has described in other threads and in "outside the box".