exactly, I have mine disabled as well. If you cancel, backup is corrupted meaning that if you need to get things back in a hurry you're screwed.
For me, it's best to start factory restore/vanillia since I like to jailbreak via quickpwn.
Here are other reasons backup is not needed for me ever. I have other work arounds.
-just use the "app backup" (from cydia) to backup specfic appstore that have important data. (wine log is mine)
-I use itextuploader to save SMS
-All my mail/contacts/caledndar are in the exchange cloud via
mail2web.com - Pick Up Your Email