I've seen a fair amount of users use browser benchmarks to measure browser performance. However I don't understand why browser benchmarks would be that useful. A fair amount of them (e.g Octane, JetStream, and Kraken) use numbers with no (seemingly) assigned meaning and the explanation of their benchmarks feel vague to me. It just seems way more reliable to check memory (the core program, extensions, and HTML/JavaScript objects themselves), CPU and GPU usage, and the source code to compare performance. Not all browsers function the same, however, so it's really not a good idea to compare them directly anyway.
EDIT: I meant browser benchmark sites, not browser benchmark themselves. I need to stop mistyping titles…