From the RePEc blog (Easing the life of referees):

One of the more boring tasks a referee faces is to check the algebra of a submission that looks promising. This is often trivial to do but may be quite time consuming, and it requires concentration. Given programs like Mathematica, the task can be simplified by asking authors to give their calculations in machine readable code. This would render it easier to do such boring checks and would, at the same time, help authors to avoid mistakes.

Mathematica is, however, too expensive. Is there any freeware that could be used for such purposes? If so, RePEc could recommend using it as a standard. This would ease the refereeing process. Referees could concentrate on contents rather than being immersed in ultimately trivial calculations. Such a program must of course be able to do symbolic calculations, like forming derivatives or evaluating symbolic equation systems.

Why are referees of theoretical papers expected to check the algebra? Referees of empirical papers are not expected to check the statistics. Otherwise, we'd be given the data.