Fonts are protected by copyright law. There has been quite a bit of tussling in the professional design and print community about whether or not it's OK to give copies of a font to someone else who works on a document--for example, if I buy a font as a designer, and use it to create an annual report, is it OK for me to give a copy of it to the printer so that he can print it? If the answer is "yes," does that also mean it's OK for me to give the printer a copy of QuarkXPress so he can print my job? (Font collections can cost thousands of dollars--far more than the cost of programs to do page layout.)
The advent of PDF has really muddied the issue In the past, designers, pre-press houses, print shops, service bureaus, and other companies have legally been responsible for buying copies of the fonts they use, even if many people do illegally swap fonts around without a second thought. Companies that use illegally copied fonts can and have been sued.
But with PDF files, I as a designer can buy a font, then create a press-ready PDF with embedded fonts for the service bureau or printer--and the font maker doesn't need to buy the font as well, because it's embedded within the PDF.
So the font creator potentially loses a sale. Print shops and service bureaus spend a LOT of money on fonts (at the time I was doing prepress work professionally, the company I worked for had spent approximately $17,000 on fonts alone).
Some companies, like Adobe, allow their fonts to be embedded in a PDF and don't mind taking the potential hit. The service bureaus and print shops likely buy their fonts anyway, because they don't work only with PDF files, and need to be able to accept source files as well.
But the makers of exotic fonts, particularly small font shops that don't offer ten-thousand-dollar font libraries and don't sell to hundreds of thousands of customers--feel the pinch more strongly. If you sell perhaps a hundred copies of a font a year, every lost sale hurts. You might not want to allow embedding your fonts in a PDF because you might want the print shop or service bureau to buy a copy of your font.
In my experience, the fonts that have the permission bits set to prohibit embedding are invariably exotic or special-purpose fonts sold by tiny companies that you've probably never heard of. These companies can't afford to lose even small numbers of potential sales, and typically are only barely surviving financially.
