Required, no......, but many find they have some advantages.
I like the that they keep the slide ceiling cooler from direct sunlight, minimize moisture intrusion when closing slides in rain, don't have to clear off slide roof prior to closing, and protect the horizontal wiper seals.
Some can be a bit noisy with high wind, and can 'pool' rain water if not adjusted properly.
Bob
__________________
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)