Generally speaking, individual SOLs might be sent on detached duty as flagships for small squadrons on foriegn stations, such as during the Mauritus Campagin. Usually these were older vessels of 50 to 60 guns no longer suitable to stay in the line of battle. There were some occasions when a fast SOL might be detached from a blockade to make an inshore sweep, but this was usually considered work for frigates. I'll try to dig up further examples when I get time.