Supplementary is a related term of advantageous.
As adjectives the difference between supplementary and advantageous
is that supplementary
is additional; added to supply what is wanted while advantageous
is being of advantage, beneficial.
Additional; added to supply what is wanted.
Being of advantage, beneficial
* 1900 , Joseph Conrad, Lord Jim Chapter 32
*:Jim took up an advantageous position and shepherded them out in a bunch through the doorway.
* gainful; profitable; useful; beneficial; behooveful