I was a kid then but my memory of 80286 was:

* Turbo was default ON and was the regular marketed speed the cpu was designed to run on, for my (dad's:) PCs it was 12 and 16mhz I think

* Turning turbo off reduced speed significantly for software written with original cpu timing in mind (I think 8088 but that was just outside of my direct experience).

So perspective on turbo button is a little bit philosophic, is it half full or half empty:). But it did not give you any EXTRA boost, like over clocking OVER manufacturer design cpu speed.