in general yes. If your fish are healthy theres no reason to keep salt in all the time. Salt is excellent for ich, abrasions, certain parasites and some other diseases. It helps the fish heal and releives osmotic pressure from wounds.
Some people use it as a preventative, but its not necessary. And when you do, you need to keep the salt content relativley stable when you change the water.
Also some fish are more salt tolerant than others. So be sure you know your fishes salt tolerances and when you do use it keep track of how much you have in there.