So although you’ll have 2 libraries, you won’t use twice the disk space.
(You will use a little though for anything that is specific to Photos).
To further muddy the waters, if the i Tunes Music folder was created by i Tunes 8 or earlier, then it will retain the older name (i Tunes Music), even if you update to a newer version of i Tunes.
I hope I've caught all of these little discrepancies, but if you come across one I missed, please drop me a line so I can update this document.
The i Tunes library doesn't have a practical size limit; as long as there's space on your drive, you can keep adding tunes or other media files. If you're not paying attention, your i Tunes library can quickly take up more than its fair share of drive space.After a lot of doubt and long consideration of alternatives such as Adobe Lightroom, I finally switched from Aperture to the new Photos app in Mac OS X 10.10.3 – and to the i Cloud Photo library too. Here’s a quick overview of my pain points and how I overcame them.Unfortunately, the Apple’s official page didn’t answer all my questions. Good news: it’s non-destructive and it doesn’t require double the disk space!Moving your photos from Aperture to Lightroom is not difficult.Your adjustments won’t translate (workaround here), but moving to Lightroom certainly doesn’t mean losing control of your picture collection or sacrificing all the keywords and other metadata you’ve added in Aperture.