It is a powerful tool to quantify how some amount changes when another number changes, such as to understand how the number of independent claims in a litigated patent influences total outside counsel fees — to calculate the correlation between one set of numbers and the other (See my post of Jan. 14, 2007: variance in an independent variable explained by correlation.).
Many correlations have been mentioned on this blog (See my posts of April 5, 2005: innovation and law department size; May 10, 2005, Sept. 10, 2005 and Jan. 3, 2007: effective billing rates and law firm size; Sept. 10, 2005: law firm size and rank on league tables; March 10, 2005: stakes in patent litigation and representation costs; Nov. 20, 2006: size of law department and number of law firms retained; Oct. 23, 2005: law firm size and overhead costs; July 2, 2007 (two posts): market capitalization and both number of in-house lawyers and total legal spend; June 9, 2007: department size and size of law firms it retains; and Nov. 28, 2007: average years of lawyer experience and total legal spending.).
Wherever there are benchmarks there could be correlations, although usually the analysts fail to push that far (See my post of Feb. 12, 2008.). Unfortunately, mathematical correlation does not prove causation (See my posts of Jan. 27, 2006: cause and effect; July 4, 2006: empirical studies of law departments are needed.).