Here's what "consolidate" does (from iTunes' help):
Depending on how you imported items into iTunes, some items in your library might be stored in different locations (in another folder or on another hard disk, for example).
You can consolidate all the files in your library in the iTunes folder—for example, to make it easier to move your library to a new computer.
- Choose File > Library > Organize Library.
- Select “Consolidate files.”Files remain in their original locations, and copies are placed in the iTunes folder.
- To create folders (Music, Movies, TV Shows, Podcasts, Audiobooks, and so on) inside your iTunes folder, and place all your imported media files in the appropriate folders, select “Reorganize files in the folder ‘iTunes Media.’”