Apple LaserWriter 12/640 PS - Manual (Page 300)

For example, if a document uses 12-point Times, available in that size as a
bitmapped font and as a TrueType font, the system uses the bitmapped font. If
a document uses 4-point Times, the system scales the TrueType font to that
size, because a bitmapped version isn’t available.
Using only TrueType fonts produces a closer match between the appearance
of type on the screen and on paper. However, a document you’ve already
created with bitmapped fonts will be reformatted with the corresponding
TrueType fonts, and line breaks in the document may change. Similarly, if a
document is created on a system that has TrueType fonts or Adobe Type
Manager software installed, it may have different spacing, kerning, and so on,
when opened on a system that doesn’t have TrueType fonts or Adobe Type
Manager software.
Keeping two font versions available
If you have a TrueType version of a font, you don’t need a bitmapped version.
However, although keeping both versions of a font takes up more disk space,
there are several advantages to doing so.
Bitmapped fonts are hand-designed: a graphic artist planned each character
in each font to look good on a screen. TrueType fonts are scaled by the
computer to match what you request. At smaller point sizes, the bitmaps may
appear sharper.
Additionally, scaling fonts takes time—sometimes up to several seconds in
slower Mac OS–based computers—but all Mac OS–based computers can
display a bitmapped font instantly.
301 Using Fonts With the Printer