There is not only Scala OT—which is an enhanced OpenType version and combines a number of the dated postscript fonts, e.g. expert (arrows, ligatures, …), lining figures, small caps in one single font, with intelligent linking; but also Scala Pro—which is an even more extensive font, also in OpenType format, with additional language support.
You don’t need the latter if you don’t have to deal with Baltic, Central European or Turkish text.
(Same goes for the Sans, of course.)

See also this thread.