Correct. Unless you really know what you are doing, or as a matter of urgency need to test something specific, then it's advisable not to have "proposed" enabled on the development release.
An example during raring was where certain libraries needed for multiarch support build for some architectures but failed on others. people with proposed not enabled saw nothing, as the packages didn't move to released until they were fixed. Some people with "proposed" enabled ended up with either broken multiarch support, or by accepting upgrades from proposed that they shouldn't have caused multiarch support to be removed completely. In turn that ended up with things like googleearth, skype, crossoverlinux/wine and more etc etc being nuked or not running.