In keeping alive or creating the threat of an invasion/future invasion as a possibility would have caused the diversion of some troops. The key thing was showing Stalin that the western allies were doing something...whether or not Stalin would have thought it as ‘enough’ is hard to know for sure.
Perhaps is was an expensive way to show Stalin that the western allies were doing something. And as you said, it would keep alive in Nazi minds the possibility of Allied invasion across the Channel.