You can, and many of us do, but you need to do some work first.
First job, which is optional but advised, is to sort through your library and get rid of duplicates and unwanted tracks.
Then, decide which tracks you want in the cloud, and set up a library with just those tracks on. There are many ways of doing that, but I did it when sorting out my library, using home sharing to import them onto a different computer. Then you rn match on that library.
What you do with your main library is u to you. Some people are keeping their main library intact whilst having th paired down library for match. The issue I see with this is that you have to effectively try to keep elements of the two libraries synced.
What I have ended up doing is having my main library on match, containing about 27,500 tracks ( including iTunes purchases), and a separate second library containing the rest, which is not matched, but can be listened to using home sharing.
If that all sounds like too much effort then you are probably correct, and at the momen I'd recommend not using match.
One thing to remember is that iTunes purchases are not included in the 25,000 limit so if you have purchased from iTunes you can go over that amount.
Thanks Keith. Yes that does sound like a big job. One thing I was thinking about was creating a second library (I think you have to choose which library is active by restarting iTunes and choosing on reboot of the program?) With the stuff that I'd want to be matched. But it seemed like that would create exactly the problem you describe - I'd want any new music i get to be matched, so that new library would need to be active. And when I wanted to access anything in the main library, I have to restart iTunes. Clunky and asking for trouble, it seems... arg.