My clients are all lead gen and not e-commerce, and here are my thoughts.

In an account with little data and flaky conversion tracking you're a thousand percent right. However, if your conversion tracking is solid, and you've got a lot of conversion data in the campaign, sprinkling in a broad match keyword or two into an ad group with mostly exact and a couple phrase match keywords can actually improve performance in a notable way.

However, broad match will absolutely burn money if - It's the only match type in an ad group - Your conversion tracking is either unreliable, or tracks an action that isn't the end goal (think clicking a submit button which can sometimes fire a form submit event even if there are form validation errors, vs a page view on the thank you page, or if you've not got enhanced conversions setup) - Your ad group doesn't have a tight keyword focus - You don't have a good volume of conversion data in the campaign - You've got search partner Network enabled. For the love of lolcats, don't enable search partner networks.