Library vs stage movieclip placement

so i have a document class with added_to_stage handler, and when i get access to stage is there a difference between:

having few movieclips on the stage ready for use, or pulling these same movieclips from the library?

is there a reason why i should be pulling them from the library (and i dont mean multiple instances, just single item of each) when i can “leave” them on stage and get them directly?