Specialist certification acknowledges you have the expertise to work with
Microsoft Office programs. Office Specialist-certified individuals report
increased competence and productivity with Microsoft Office programs as well as
increased credibility with their employers, co-workers, and clients. Office
Specialist certification sets you apart in today’s competitive job market,
bringing employment opportunities, greater earning potential and career
advancement, in addition to increased job satisfaction.
(from Microsoft Web Site)
MCAS Certification is achieved per
product within the suite - you become certified in "Microsoft Word version"
and so on. Once you attain certification in the group of products within
the suite you are considered Master certified.