When you are creating a new background or sprite, the list of fonts there are to create said background or sprite are very limited. It would be really nice if you could add more.
Support for seeing a few extra fonts, since I think some useful fonts that Scratch that it lacks includes a second sans-serif and serif style font along with a monospace font. There technically is a way to get it so that any font that's on your computer can be put onto Scratch using this method or you could just write some text using an external program such as Inkspace and then convert it to an object so it can render properly in Scratch, however both of those methods are difficult in comparison to just using the font selection that the Scratch costume editor provides.
The more fonts they add, the longer Scratch would take to load