Salt is added to aquarium to improve the slime coating of fish and to prevent parasitic infections. Many aquarium fish tolerate salt.
Plecos too can tolerate salt by to a very small extent about 1 tablespoon/30 gallons.
Plecos are generally more sensitive to salt than other fish.
If you have plecos in your aquarium do not add salt to it. The risks outweigh the benefits, if any.