Gregory,
Some do it so that the Westy pop tops fit in garages.  VW did it in ~87-88 as
a factory made with the Wolfsburg lowered springs.

There are many reasons...

I put on the H&R springs to improve the handling in curves and unexpected
sharp curves.
For me, my 88 Wolfsburg leaned too much in curves.  I wanted to be able to
take the curves without slowing down and be prepared for sharp, unexpected
curves (you find them in NC often)

The springs lower the VW lowered suspension by about 1" in the front and @2"
in the rear.  The front clearance did not change because the tilt was removed
so the front is the same as the VW clearance.

I was able to get about in the snow in NC during last winters big snow storm.
 I removed the front spoiler to avoid damage and put it back on when the snow
was gone.  It never bottomed out and for the most part got around OK.

While the springs are a bit stiffer than the stock, it only is harsher on
BAD/bumpy roads otherwise they are smooth.

H&R also recommends removing about 1" of the bump stop to restore wheel
travel.  It can be done in the rear, the front maybe, I will look into it
when I replace some worn front bushings.

It does not bother me.  I am used to the ride. It handles better around
corners and curves. I do not feel the van leaning as before.

I have had over 1000 lb. of people and gear on board and the van went down
maybe 1/2" in the rear.  The handling did not change.

I like the springs for the most part.
You have to decide what you want in ride comfort.
The one thing I do miss, is the ability to get under the van easier with the
higher old springs without ramps.  Now I just lift it up a bit with the jack,
no big deal.

Robert