If you're concerned about bandwith, then you should know that when iTunes match streams music to your Apple TV it's doing so over the internet, so if you're bandwith capped then you may take quite a hit if you listen to a lot of music.
iTunes Match only matches if your music is on the iTunes Store. Many classic CDs have been re-released over time, and your version may not be on the iTunes Store. Typical problem with Beatles, Genesis, etc. Many CDs come in different versions in the USA and Europe; typical result is a CD where everything except a single song is matched.
All in all, 85% of my music was matched. And that included songs that I manually imported from LPs. And what wasn't matched got uploaded, so there's not really a problem. You just don't get the upgrade to 256KBit AAC.