The big money claims come from personal injury. If your ladder falls or pole snaps & hits someone on the head then the resulting claim could be huge. Property damage is an issue, but its rare the money gets big on that side of things. I have €6.5 million cover for €600 per annum which covers me for property worked on (many policies don't!) and covers the use of ladders, access equipment, pressure washing and office/shop cleaning work.
Many of my commercial contracts require a copy of my insurance details, and even when it isn't requested I always include it with the quote pack as it helps convey the professional image I want for my business.