Lost libraries due to auto sync

Hello,

So after I connected my iphone to itunes i pressed the x button that stops the auto sync that launches when the device is connected. And, I noticed that all my music had disappeared from the device. After doing my research on similar problems i could not find a solution to restore the libraries on the device. I ended up spending hours remembering what was present in my device's libraries (music, videos, voice notes..) and I added them back manually which was a pain in the a**. My question is: does anyone know why itunes performs the automated backups and syncs everytime we connect our devices (which take an incredible disk space btw) and we cannot seem to find these backups when we need them? we only find the backups we once performed manually by choice(manual backups with a date next to them). I might be missing something please share your thoughts to help.

Thanks.