CCB files are simple Plist-files with a ccb extension. It is human readable (text/xml) and you can easily edit it manually if required. For example, I sometimes will generate several scenes based on one ccb file using a simple script. The format is well documented on CocosBuilder github page.
One distinction, is that Sticky Notes which are meant to be displayed in CocosBuidler are only found in CCB files.
CCBi is a binary format meant for publishing.
It is a binary file format designed to be as compact as possible and very quick to load.
The binary format is also documented by CocosBuilder.