InstallLib DLL confusion

I was looking at the Library Installation section but I could not find what exactly InstallLib DLL ..... does?

I am mainly asking this because so far I copy my non-registered DLLs to the respective file and that is pretty much it. Is InstallLib DLL increasing some counter in the registry? what is it used for?

Thanks

I am mainly asking this because I would like to know the difference between using

File \a "boo.dll"

and

InstallLib DLL NOTSHARED NOREBBOT_NOTPROTECTED "boo.dll" ......

any guidance?