Obviously if you copy them when importing then you will take up more hard drive space since you will now have the items in two locations.
why two locations ?
assuming you have
copy files to ... when adding to library checked in preferences > advanced, iTunes will copy files you add to the iTunes music (or media) folder. when done, you can delete the
original files from your HD.
although i don't use iPhoto as extensively as iTunes, i expect it will be similar with iPhoto
Whats are your preferences and why?
you can run your complete iTunes library from an external HD. simply copy the
entire iTunes folder (not just the iTunes
music folder) to an external, hold
option while launching iTunes and, when prompted, click on
choose library and select the iTunes folder you moved to the external. when satisfied that all works as expected, you can delete the
content from you local iTunes music folder.
or, you can split your iTunes library across various drives. for example, you could have all your music locally, keep movies on external HD (A) and your TV shows on external HD (B).
if you want to move selected content to another location, simply do this
(a) iTunes > preferences > advanced. temporarily point
iTunes media folder location to e.g. external (A)
(b) select (highlight) e.g. the movies in iTunes, right-click (or ctrl-click) and choose
consolidate files from the pop-up menu. this will
copy the selection to the external. when done, you can delete the
original files from <MacintoshHD>/users/<yourname>/music/iTunes/iTunes music/movies to free up space on your internal HD.
repeat to move you TV shows to external (B)
(c) point
iTunes media folder location back to your local iTunes folder if you want to add music to your internal iTunes folder.
with content on one or more external HD(s), you need to make sure they are mounted on your desktop
before you launch iTunes.
AFAIK, you cannot split your
iPhoto library but you certainly can move it to another location. find the instructions in
this support article.
