yellow other and streaming music

My apologies if this question has been asked. I see quite a lot of threads on the "yellow other" that shows in itunes when your phone is connected. Like many others mine seems to grow a little everytime I connect and sync. I followed the instructions of other threads to go into settings>general>usage to see what size some apps are. I was surprised to find over a gigabyte of music, when I have no music stored on my phone. So I deleted music. Sync'd my phone and the yellow other dropped is size dramatically.  Then I listened to some music by streaming it from icloud as I have done since I got this phone. After an hour, I check the same area and there was music again. Several hundred megabytes worth. So my question is why does the music app grow in size while I stream music? Or I am guessing now, that I am not really streaming music am I?

Thanks for any clarification