Being a "newbie", I note that the pick ups on my bass are sprung. Are they intended to be height adjustable & what are the benefits between high & low?
Basically as much as I know

the higher they are the higher the output.

too much of this can be bad, ie if you have open pole pieces the string can easily be struck to the pole piece and make a ugly sounded clank

if you don't... try to keep the Pups away from the strings path with you're playing quite hard/slap
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If you don't know how to go about this then leave them as they are for now, you can always take your bass to a store and get a set-up.

Also regarding the question itself about the pickups, they are adjustable because depending on the type of sound you're looking for you can get them out with just adjusting the pickups.

Say me myself i like my low notes sounding more than my high notes that's why i put them sort of like sideway going from up to down like \ (well not with that angle tough but i think you get the idea hehe).
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pick-ups are pre-set at the factory. learn as mush as you can before doing any adjustments yourself. here is a good place to start.
The height just varies the output, like the guys said previously. Usually there is a screw at each end of the pickup; loosening it increases height, and tightening it decreases height.