If the wind turns them and the wind pressure on one side doesn't interfere
with drafting air up and out, that's cool..
But, around here there isn't a lot of wind on many of the hotter days..
Average wind speed here over the last 7 days is 0.5 mph
WOBURN WEATHER CENTER - Weekly Conditions
During the day, it's about 2 MPH sometimes.. In the winter, we get a lot more wind..
And that's when I don't mind some hot air in the attic.
However, if it's turning when the wind isn't blowing..?. That means the hot air
that's drafting up out of the attic is doing
work.
Which means the air flow is being restricted, slowed down.
IMHO, a long ridge vent on the apex has got to be the best way to vent.
But it needs some air input in the soffit area to work best.
Sadly, my house didn't get any over-hang/soffit area.
My ridge vent spacer material is a plastic mesh cloth (like a pot scrubber).
I'm pretty sure it's the worse type to use, if you want good air flow.
The roofers has installed a real nice open-air-flow vent,
but they didn't have the proper size cap shingles to cover it.. Had to replace it with mesh junk..