Clarifiers work to "clump" dirt to filterable sizes. The Miraclear has some Copper sulfate in it as an algacide. I don't mention "use it" because I don't want to cross the fine line of "selling". But I did say, you don't NEED it in a clean, clear pool, but if you need a clarifier, by all means, it's a fantastic product, according to what the service company feeds back to me.
Personally, I have never had to use it on my pool, but I have used it on my cousins out-of-control pool and it does work.