Aggregates are useful; otherwise we would have no purpose for concepts like “the structure of production.” The task, however, is to see which aggregates are useful, and when it is useful to deaggregate. Of course, too much deaggregation can be just as useless and unnecessary as not deaggregating at all.
The bottom line: there is no deaggregation vs. aggregation dichotomy.
(I would disagree, however, with parts of “Lord Keynes'” post, since gross domestic product, or even any output aggregate, is not necessary to know the merits of letting individuals of the market deal with industrial fluctuations without exogenous intervention. This brings into consideration Lachmann’s [borrowing from Hicks] dichotomy between catallactics and plutology. If we are studying catallactics, then the end should not be to conclude via output, but to conclude via exchange. I would agree, however, that oftentimes even Austrians [even myself] are marred in the plutological approach.)