Does anyone use those little pop on clips?
PITA to get on and off. Suppose they are to protect loaded rounds if the magazine is dropped. They just seem to get in the way most of the time.
From what Magpul says, the covers are to protect the ammo from damage in storage and transit as well as free of dirt, debris and other crap that can keep the mag from working.
I find them a little tricky to put on, but taking them off is really easy.
When you use mag pouches on a carrier/belt, which end of the mag goes down? The open end. That provides all the protection those mags need -- no covers to fumble with.
But, if the loaded mags are in storage (ammo can, range bag, ...), maybe the covers serve more of a useful purpose.
I'd remove the covers once I put them in a pouch -- mainly because they might not fit or could catch when trying to remove the mag from the pouch.
This guy shows how quickly you can remove the covers: