People usually qualify it as a good thing because it means you have good calc/alk/mag/lighting. Pretty much means that you have a tank that can support stony corals very well.
Many people also like the way it looks. It grows flat, looks nice, and does not cover coral tiissue.
Personally, I like the way it looks when you have liverock randomly covered in all different kinds of coralline. However, it doesnt look as nice when its 100% covering the rock and a solid light pink. I just want to be able to keep it in check. I like the look when coralline only covers 30-40% of the rock in random patterns with different coralline types.
Mainly I do not want it because it grows on the tank walls and bottom (mine is bare bottom), and it is harder to remove on acrylic without scratching. Once it reaches critical mass in a tank, its there to stay and can become a pain. You can scrape it off the glass every day, but you arent going to make any advancement in the fight because you are scraping off thousands of flakes of coralline that will eventually just settle somewhere else and start over.
This is what I am trying to avoid. If possible.
I tried to buy base rock in my previous 75, but in no time the coralline took over the whole tank. Even if I missed a little bit on a few frag plugs, it took over.