When I went into this enterprize my first contact and supplier of nucs with now some 5-600 hives told me he didn't use them.
The guy lives and operates in south LA near Baton Rouge and it get plenty hot there, and, here where I live.
So I don't use them either. Actuall the bees will glue the covers, whichever you use, to the hive box and that will prevent wind from blowing the cover off. If the INNERCOVER is used the bees will glue that to the hive box and the outer cover will be loose.
The INNERCOVER does have a cutout that does provide for some hot air to rise up and escape to aid in ventilation of the hive. I dunno, my bees seem to have been OK last year and OK so far this year.
Just think, bees are hidden everwhere in nature with no INNERCOVERS, or, outer covers for that matter.
I have found that INNERCOVERS are useful in keeping the bees down in the box until one can place the outer cover on without smashing too many bees. Take the INNERCOVER, place it on one end of the box, level, and slowly slide it on, nudging the bees out of the way until the opposite side is reached. Then quickly place the OUTERCOVER on.
Hope this helps but you'll mostly always squish a few bees. There are other tricks to use to keep some good bees down but those are different stories for different times