An MTC provides traceability and assurance to the end user about the quality of the steel used and the process used to produce it.
Typically a European MTC will be produced to EN 10204. High quality steels for pressure vessel of structural purposes will be declared to 2.1 or 2.2 or certificated to 3.1 or 3.2.  (EDIT: type is declared not by chapter in the document, but by type name, so edited the numbering)
The MTC will specify the type of certificate, the grade of steel and any addenda. It will also specify the results of chemical and physical examination to allow the purchaser or end user to compare the plate to the requirements of the relevant standards.