I have the utmost respect for life, that is why I now protect my fish, my corals, my CUC, from what I believe are problematic creatures. I used to wonder why I lost fish at times, snails, corals retracted. I took some advice from some really experienced reefers who suggested to me if I don't want to lose stuff, make sure about what you put in your tank.
Forget the CUC, concentrate on water from source to tank, make it absolutely perfect consistently and you don't need the CUC's I am so happy with this advice. In this last rebuild, now more than 18 months, no deaths of fish, no deaths of coral, corals expanding nicely, not even a snail is gone, some coraline algae, but none else.
Each person has his./her own ideas of what should be in their tank.
Granted, many creatures are or may be beneficial, how many times have I heard the statement, worked in my tank! What works in some may not work in others. Many of these small organisms on their own are not an issue, but then they multiple and can be hard to eradicate.
Just my 2 cents...