The relatively low (and I have to tick boxes for most of the high risk industries on the form) amount that I pay each year for what seems to be a nice PI policy is easily worth it for the peace of mind.
The requirement for the policy some clients have are only there because they're multinationals and it's a company-wide policy. Local clients never expect contractors to have a policy.
I think at my current premiums I would need to pay insurance for 100 or 1000 years to even get close to the sort of numbers that get thrown around for a day's worth of damages on some of these projects.
The likelihood is absolutely that nothing serious will go wrong, that if it did it wouldn't make it to the courts and furthermore that if it did it wouldn't be negligence of any kind, or was covered within the contract itself.
But the thought of having skipped out given the possible consequences; No thanks, value my sleep too much.
As things are now, I'm mandated to spend $XXXX/year on insurance that I've never used and know, for a near certainty, that I'm never going to use. I'd really rather not. I've looked at the statistics and, for me, it's a better bet to eschew insurance. (Which, generally speaking, it would have to be, otherwise the insurance industry would be losing money.)
That's what most people say right up until they make a claim.
I'd even pay good money for (de facto-) fake insurance, just so mandates and overly-bureaucratic clients/partners leave well enough alone.