I did some light reading just now and it seems that its mostly used in black powder or straight walled cases with cast lead bullets if at all and is pretty much abandoned in modern shooting.
Seems like nowadays we can choose a powder to give proper case fill and not rely on what is available at the 1950s gas station that requires the use of a filler to make up case volume with something else.
I guess I should have added that they are typically used to compress loads and I have never seen anyone compress loads with a filler...and its still a practice today...just not for me or anyone I know.
I know Gemtech and S&B use it in their 300 blackout subsonic loads. It damn sure makes a mess in an ar15 lower with a suppressor attached. I don't buy factory subsonic loads anymore for that reason alone.