Although my theme has a minimize button, I think didn't use for more than a decade. If you need space go to a new desktop. And organize your files in you home directory sub-folders, if you need temporary space, use /tmp which will delete it on the next boot (beware of privacy issues if other people are also using your computer).

Since I got used to multiple desktops, I really don't see much value on the minimize button. I makes harder to use the app. If I want to alternate to another app, I just click it or alt-tab to it; minimizing it makes it harder to alternate to.