Michael, I heard you describing that one last night (in the Glancy tank) - that might have been a Eunicid worm... and yes those need to go but they are very rare.
Bristleworms/fireworms - GOOD FOR YOUR TANK. Not good for your fingers (fireworms *really* hurt, bristleworms just hurt).
Older literature suggests removal because at the time, their role wasn't understood. Those of us who live in the 21st century know how beneficial they are.
Love thy worms.
If your rocks "come alive" with them when you feed, you're feeding too much. If you see the odd one when you feed, no biggie, but if your tank is "overrun", cut back on their food, their population will decline appropriately.
Because they will clean up dead tissue, they are often perceived as the "cause" of something dying. Not so, IME. If it's dead, or dying, they'll clean it up. If it's healthy, they will leave it alone. They are scavengers, not predators, for the most part.
Eunicid worms are a different critter entirely.
The ONLY time I suggest ridding a tank of bristleworms, is dwarf seahorse tanks - H. zostrae. I have personally witnessed a bristleworm help itself to a dwarf hitched to a piece of caulerpa... not cool.
Otherwise, they are 100% beneficial.
Jenn
Theirs I think was in a 125, so it could have got some size to it, and it ate quite a few softies before they caught it in the act.