This is separate from the matter of stories be made up of stuff stuck together, which I pontificate about here, but about stories, however long or short, that are complete in themselves but which use the same setting, or characters. Trilogies that really are three books, and not just a book conveniently bound in three covers. A series of shorts that may or may not turn into a fix-up but clearly could do it.
On one hand, it leaves the story cabined, cribbed, confined, bound in. Some people -- I've heard them -- complain that it means less invention for the new story. What I tend to note is that it means that the story can't evolve purely out of its own nature to dictate the setting. And then you get conflicts. . . which sometimes are a challenge but sometimes require you to cut loose the story and reshape it, and scrub off all your own serial numbers for a new setting.
On the other hand, it does let you develop the work further. And raises philosophical questions about whether the series as a whole is a work in itself and not to be judged solely by its part. And allows you to stifle the impulse to show all your work with the knowledge that it might be a story later, and lets you fill in the background details with more detail because -- you already invented it all the way over here. . .
Of course, that requires that the inchoate story ideas that appear to be the same setting actually develop into full blown stories. . . .