what size tank?
they are very useful, some don’t use them but most do, you are unlikely to see amazing results but it all helps, and each time you empty it you will see all the dirty muck that would have been in your tank, they also are useful for gas exchange, helping oxygenating the water, these are the things you need to do before adding chemicals, try and prevent issues by removing nitrates, phosphate etc rather than having them in there and using a chemical to remove them, as the issue will come back if you don’t fix the reason they were there In the first place, preventing the problem is better than trying to cure the problem and a skimmer is a good preventative measure.