I was asked for 12 months' worth of statements for a place I wanted to rent in Islington. I got them printed out at the bank, and then spent an entire day with a Sharpie and a ruler and redacted every payee and amount in each of those statements. The approved my rental contract without a peep.

A potential employer once also wanted statements - I think 6 months' worth, and I did the same. HR pushed back but legal backed them down rather quickly. I think these people ask because most just comply without question.