A standard reference

There is often a tacit understanding that a corpus constitutes a standard reference for the language variety that it represents. This presupposes that it will be widely available to other researchers, which is indeed the case with many corpora - e.g. the Brown Corpus, the LOB corpus and the London-Lund corpus.

One advantage of a widely available corpus is that it provides a yardstick by which successive studies can be measured. So long as the methodology is made clear, new results on related topics can be directly compared with already published results without the need for re-computation.
Also, a standard corpus also means that a continuous base of data is being used. This implies that any variation between studies is less likely to be attributed to differences in the data and more to the adequacy of the assumptions and methodology contained in the study.

If you haven't already done so you can go on to read about other characteristics of the modern corpus:

Sampling and representativeness | Finite size | Machine-readable form