custom properties - wanting to expand my knowledge

I want to understand better how I can utilize some of these custom property options, but haven't found the time to test them all. I know you guys are busy building the future, but at some point it would be awesome to have a readable document that explains more of this. What kind of Custom Properties can I add to annotations? Item Variables? Folders? and when would you use Multi Line text? User? email? URL? obviously these are here because they're useful to someone, but I want to understand how.

Also, everyone please share any awesome customizations you've figured out that have helped your own workflows.

Thanks!