A few authoritarian regimes have been known have high voter turnout. Russia recently had 67% turnout, Cuba 90%, Turkey had 85% though turkey is compulsory. So, turnout is kind of an independent index.

Also, statistically speaking, if the turnout is “representative” then high or low makes no difference with regard to what would occur with full turnout.

When people say we want high turnout, I think they really mean I want my side to have full turnout and the opposition very low turnout —as this is the only situation where this quest makes sense.