What are the benefits, pros and cons, of HBN hexagonal boron nitride coatings?

This discussion applies to both bullets and barrels, and to stainless and/or normal steel barrels?

For example,

I've heard that HBN can increase velocity and can also stabilize velocity for "cold barrel" first shots that pattern with the rest of the shots.

On the negative, I've heard a rumor that Krieger Barrels frowns on HBN and recommends against it.

Never heard of this one, but like all the other snake oil applications to rifle bores over the years that come and go, no barrel maker will endorse them, for several reasons.

I use it a lot.
It lowers friction and usually needs a little more powder to get speed up to normal.

Cons:
It takes time to apply

Pros:
Way less CBS "jump"
Way less cleaning