Coralline algae growth is an excellent visual indicator that your tankwater chemistry is in line.
It's a sign - and a beautiful sign at that - that your pH, carbonates and calcium, along with other factors are where they should be ~ or at least very acceptable in most cases.
Also - as mentioned - many people find that it looks nice in a reef tank.
It may out compete other nuisance forms of algae as well.
It's nice to have - and a good sign things are going well in there.
Coralline or the lack of coralline is by no means a sign that you are doing everything right or wrong - and many fine looking tanks do not have it. I've seen some beautiful tanks that are totally void of the stuff ~ doesn't mean the tank's not nice or well taken care of either.
A tank can be dead nuts perfect - and not have coralline algae growing in it. A matter of personal taste - as always.