Sparkie,
Odviously, being a large rubber boot, it is there to keep both dust and water away from the bulb. But, it also keeps a bunch of heat in there.
I have had more then my share of problems with some poorly built H4 Silverstars made it on the market for sale. 4 this yr alone. Low beam wire weak. All replaced free at Wally World, and 2 from SS for my troubles.
So I have been running without the boot, and other then a little more light coming out from behind, It is a toss-up if you really need it.
Even after a hard rain, there was no water in that area, and new lithium electrical grease in the socket, does a fine job protecting the electrics.
So go commando or bag it, your choice, and skin.
Ride safer all, and ATGATT please.
Greg