What does the recipient see when they don't have the same TTF? Missing characters or character substitutions.
What's sad is the PTC could, but chooses not to**, define each character as a procedure and then call that for each place it is used, then stroked in place, significantly reducing the file size. This is applicable to HPGL, Postscript, and PDF. A single "font" character takes from 2 to about 10 coordinates, while reusing a defined procedure requires 1 coordinate and 1 character to select, for a reduction averaging 5:1. It's a miracle - similar to the values above.
This is essentially what is happening with TTF, but I'm pretty sure they don't embed the TTF definition into the file. At least they did not do so for the Postscript output.
They could also, but choose not to, limit the number of decimal places used to describe the geometry in the files. I think they currently use 6 place decimals, on the off chance that someone will notice a millionth of an inch difference. It easily doubles the size of the Postscript files that replace paper drawings; harder to tell for PDF, as those files are compressed. At the least they should ask.
**Up to WF 5.x.