Why would I want to turn on iTunes Match on an iOS device?

I'm a bit confused about iTunes in the Cloud vs. iTunes Match. My understanding is that iTunes in the Cloud allows me to have my songs in the cloud. I can see all my songs by turning on "Show all music" on my iOS device. iTunes Match allows me to add music to the Apple cloud that was not bought in iTunes. I have enabled that on my Mac to add music I buy from Amazon.

But why is there an iTunes Match switch on the iOS device? I cannot buy music on iOS and add it to iTunes and turning on "Show all music" already gives me all songs.