A dumb question

I moderate a small Linux firewall forum and I get this type of question often enough. Like how do I use the unused disk space of my firewall for file sharing (or other apps like mail or web server or whatever). I keep on giving the same opinion that it is a terrible idea to risk compromise of your security system to save a bunch of MB. Am I in left field or just paranoid?

Could I get the opinion of others in this field?