Value of directories

I think these basically track the packages installed by the system installer. If you delete them the system may think it needs to install them again. I'd leave them alone personally.

 

My first thought is: you sound like you're trying to go round all the hidden corners of your drive in order to delete stuff. So I will start by saying "if you don't know what it does, you should leave it there." In fact, even if you do know what it does, you should leave it there. You are unlikely to save much space by deleting any system stuff: the big savings only come from your own files.

Receipts and BOMs (Bill of Materials) are data left by installers that provides a list of what was installed.
Saved Application State is used by the "Resume" feature to ... save the state of the application.
Boot Caches are system caches.

 

As benwiggy says if you don't know what files are for don't touch them. In fact you shouldn't go roaming around below your home directory unless you really really know what you are doing.

OSx (and most *NIX systems) have all kinds of strange appearing directories and files. People trying to save space often go down and start deleting stuff and wind up with a system that won't boot.

Some of the poor quality "cleaner" utilities (Like MacKeeper) are prone to deleting stuff that the OS needs to run and you wind up with a system that won't boot.