Like all market activity, the high-level point of all that activity is to derive the real price of the thing being traded. Without falling too far into the late stage central planning thing, this is the mechanism that has been absolutely broken (due to been poorly done by pathetic humans) in all previous attempts at communism.

As a tangent, it would be interesting to see if non-pathetic modern computer systems could actually achieve to implement that mechanism successfully. But if sci-fi is to be believed, that could easily fall into another form of dystopia.