https://bugzilla.redhat.com/show_bug.cgi?id=857860
--- Comment #13 from Werner Lemberg wl@gnu.org --- Greg Hitchcock replied as follows:
The simple answer is that the gasp table was designed for and only applies when font smoothing is enabled.
The intention of the gasp table was to fine-tune the grayscale work. The Calibri font was initially only designed and hinted for ClearType, the gasp table settings and the sbit data was intended to *help* Calibri work better with either bi-level text or font smoothing.