PD uses links to files as we understand it. Also when you edit a file (e.g. cut off some pieces), the original files will never be touched.
If you have “loaded” media files into your media room from various locations, PD can still find them, provided that you don’t move these media files around.

If you have moved files around after you have saved a project, at loading time PD will give a message saying that it cannot find and do you want to ignore or browse. The latter option is valuable, because when your browse to the new file location, PD will pick up the new link and use that and thus recover your project media collection.

If you are not sure whether you will move files around after you have saved the project, or even just to be sure that you always have all the project material somewhere together, it is very wise to pack the project material. (It is in the file menu). PD will collect all media files used, and even media that are being used in titles and other features, and store it together in the (empty) folder you have assigned for the packing. The project file itself will also be stored in that folder. This is the way you can preserve you projects but also move projects between computers. Projects are preserved, as long as (future) PD versions are able to read and understand the project file.