Can I delete MobileSync back ups?

Sometimes, you noticed that your hard disk is being taken up by mysterious big files and one of them is inside library/Application Support/MobileSync . There are several folders keep growing in size here.

Yes, you can delete the files but it should be done through itunes, with your phone connected. Open preferences in itunes, select the device tab, click on the backups you want to delete and select "delete backup"

Solution here.