Don't use spaces for packages, they will work from usb with spaces but not other ways like PKG Linker (it renames them to solve this issue). So best practice with ps3 files is to use underscores for spaces.
Why no spaces, something to do with the file system, even on windows some tools will not work with spaces in the file names or paths, also if you look through the ps3 firmware you will see no spaces. In the case of PKG Linker it has to do with URLs, you could have spaces, and they can be replaced with %20 in the URL, but we decided to just rename the files with underscores instead as it can help with other tools too.