Brown Act violations do get exposed every so often and usually result in the action that was being discussed getting reversed.

Its most commonly violated by city council members because city councils are usually small, so it's very easy to violate accidentally. Say you have a five member city council. Council member A emails council member B to get their thoughts on an upcoming item. Then a few days later council member B emails council member C to ask a question about that item. That's a Brown Act violation.