What? NSP files are just used to install games onto a Switch, NSZ is the same except they're compressed versions of NSPs, they install the exact same way and they take less time to download and take up less space on your PC, but the installed game is the same size no matter whether you use NSP or NSZ
They are installable just like NSPs, they can't be ran directly.
It's possible that in the future a sysmodule will be written to support running compressed NCAs that way they could be installed without being decompressed. There have been some talks about it, but no one is working on it yet AFAIK (at least not publicly)