The PDF standard requires that all viewers render the fonts Helvetica, Times Roman and Courier --- and their italic, bold, and bold italic variants --- without them being embedded.

Given that fonts used in comments are embedded (not as subset fonts, but the whole font), significantly increasing the file size of the PDF, the ability to restrict comments to the standard fonts would be very useful.

Note that this is currently not even possible to do manually, unless you actually have a license for these fonts; While metric-compatible fonts can be used, they will also be embedded when saving the comments.