It really varies widely depending on how you use fonts:

Fonts for PRINTING: You need tons of sizes, really high definitions, as it can be printed 4" high at 300dpi. 3MB for a TTF? OK.

Fonts for iPad Games: You need TINY file size. <200KB, & won't need as high-res at all, esp. variations. You're fighting hard against the size for your game download, to get under the 50MB limit for mobile vs. wifi-only with most US carriers.

Fonts for Web: You need to ensure browser compatibility, size (for download times, which kill UX if it's slow). Too often, devs forget their homepage assets are cached, & don't see the critical first time user experience with their site as slow.)