RACOHubbell- 506 Switch Box in 3 x 2-Inch Gangable 2-1/2-Inch. Deep, Eight 1/2-Inch. Knockouts, Old work, Plaster Ears, Gray Finish

What do the side long screws do? Do they cause the metal on the side of the box to flange out and move forward to catch the back of the sheetrock ?

Do the flanges get in the way of the knockouts on the side?

Could I connect two of these vertically rather than side by side?

Will this work with 3/4” thick drywall?