I know the subject of royalties has been talked about so I found this interesting.
There are four (4) categories of royalties.

MECHANICAL ROYALTIES- These are paid to the artist, writer and publisher based on the number of recordings sold.
PERFORMANCE ROYALTIES- Are paid to the writers and publishers every time their song is performed live or played on the radio.
SYNCHRONIZATION (SYNCH) ROYALTIES-These are paid to the writer and publisher every time a song in used in a commercial, tv show or movie.
PRINT ROYALTIES-Are based on the sales of sheet music sold. (Doesn't say who they are paid to)
I can see why an artist would want to use their own songs. The writers seem to get a bigger share of the royalties.