it told the user whether the carpet was clean
In theory, it did. But in practice, the autosense was just a nifty marketing gimmick. For starters, the autosense was operated by a microphone located at the opening into the bag housing, so there was a slight delay in the autosense picking up the sound of the grit, by which time the user had likely moved on anyway.
Secondly, it did not increase motor power for debris that did not make a sound, such as dust or pet hair which arguably need more power than surface crumbs.
Using the autosense, what one ended up with was a carpet that was cleaner in some areas than it was in others - rather like a dust based patchwork quilt. Also, because the cleaner ran in low power 80% of the time (unless the user over-rided this with the boost button), it meant that the base model TP2 was actually a higher peforming cleaner than the TOL Autosense which made the TOL models a waste of money.
My godmothers parents (who lived opposite my godparents) bought a TP1000 to replace a Turbopower U2194, but they always complained that it was rubbish unless you left it on boost all the time. Using the boost feature on constant caused it to burn the motor out after a few years and it was replaced with a DC01. I'm sure the same could be said about many other Autosense cleaners too.