I'll tell you were I see the benefit of iCloud + iTunes Match (for me).
I live in Modesto, Ca, but work in San Jose, Ca (90 mile commute one way) and so its fare to say that I travel a lot for work and sometimes don't have the luxury of coming home every night.
The Old Problem:
Several years ago (2008/2009) when I had my iPhone 3G (but before I purchased my MacBook Pro) I remembered having issues with my phone and had to make an appointment for the Genius bar. The only time I had available was early in the morning before work. After determining that my phone was faulty, the Genius went ahead an gave me a replacement unit, but unfortunately that meant that I would be losing everything on my phone (until I got back home to sync later that night).
I did have MobileMe, so I was able to Sync my contacts back to my phone, but unfortunately I had no Music, and I plug my phone into my car stereo to listen to Music on my commute back home. So this made for a very boring 1.5 hr drive home.
The Benefit:
With iOS 5 now being PC Free, I can go to the Genius bar and get my phone replaced, then go to work and set up my phone, log into my company wifi and before my day is over, all of my Contacts, Bookmarks, Reminders, Calendar Events, Notes, Photos, Apps and now Music will all be re-synced back to my device (all without ever plugging it into my Mac).
I do travel a lot and lately I've only been traveling with my iPhone and iPad (the MacBook has been staying home), so for those days that I know I will be away from home for a few days, I no longer have to worry about syncing certain song before I leave, I can now just leave and download those tracks later on.
Everyone will have different reasons for wanting to use iTunes Match, but for me these are my benefits.