The practice defined
Benchmarking compares an organisation's metrics, cost per unit, IT spend as a share of revenue, process cycle times, service levels, against a peer group or reference dataset, usually to locate performance in quartiles. It can also compare practices rather than numbers, examining how better performers achieve their results.
What a quartile number can and cannot tell you
A benchmark can tell you that your cost base is an outlier and that a question is worth asking. It cannot tell you the answer, because the number arrives stripped of the scope decisions that produced it. "Top-quartile IT cost" depends entirely on what was counted as IT, what was outsourced and therefore hidden in other lines, what service levels were being bought, and whether the comparators were investing or harvesting. Two companies with identical benchmark positions can be in opposite strategic situations. When a benchmark is presented as the case for a cut or an award, the decision-ready question is always: same scope, same service, same ambition, or just the same denominator?