Font Book Helper changes the icon that's used to represent the outline font part of Adobe PostScript Type 1 fonts from Font Book's default gray icon to a red one, visually reminiscent of the red PostScript "A" icon used in OS 9 and prior. This has the effect of breaking up the grayish visual monotony that Font Book introduced, and makes fonts and font types easy to identify even at a quick glance.
Thank you! Now I can quickly look in a folder and see which files to grab. You've saved me much time and headache. Sure, the red icon could be a little better instead of just a tinted version of the old icon, but it still works.