Fontastic allows you to see what each font will make your sentence look like, and it allows you to move fonts to the trash (whereas the Finder doesn't).
Fontastic won't let you see any fonts in your fonts folder unless their names match the names their resources contain.
For example, if you download a font called "Cartoony 4" and you change the name to "Good font - use this one," Fontastic will not show this font in the list. This isn't considered a bug, because the fonts could not be removed if this safety were not in place.
Fontastic can take any line of text you give it and generate a list illustrating what it will look like with each installed font.
Fontastic also allows you to trash unwanted fonts from within the program, without quitting other programs first (which the Finder also requires).
To select a font for deletion, just click anywhere on its line(s), even though it looks like an ordinary text box.