As a longtime subscriber to iTunes Match, I can confirm this from
first-hand experience. iTunes Match is an optional and opt-in service
that costs $24.99 per year.
When a song in your library is matched with Apple's music catalog, you
have the *option* (it's completely optional and opt-in) of deleting your
own song from your own library on your device, and can download a
high-quality DRM-free version of the matched song from Apple's online
catalog - this whole process is a *manual* process.
What's really cool about it is: Apple doesn't care where your local songs
come from - they could be crappy MP3s downloaded from literally anywhere
- and you can replace them with pristine high-quality DRM-free versions
from Apple's catalog to keep forever with no additional surcharge, even
if you eventually cancel your iTunes Match subscription.
iTunes Match also makes your entire music library available for
on-demand streaming on all of your devices, which means you no longer
have to copy your music library to each of your devices or keep it
updated on them, which saves you time and tons of storage space on your
devices - space that those song files would otherwise occupy.
It all works great and is well worth the cheap $2/month fee, IMHO.
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