Conversation so far:
What is an auxiliary in the context of marching bands?
The color guard, or auxiliary, of a marching band or drum and bugle corps may contain sabers, mock rifles, and tall flags.
What did auxiliaries do for marching bands?
Many bands have auxiliaries that add a visual component to the performance.
What did the visual component of auxiliaries do for marching bands?
For ceremonial bands, this could be a traditional color guard or honor guard.

Question: What did this do for them?
Self-contained rewrite: What did being a visual component of bands do for color guard or honor guard?