Three people in the thread say they often read them. For an alternative, I'll say that I often skim them, but they're generally not very significant in my decision making process.
The candidate is generally forced to take the job description and riff from that about how their skills/experience are applicable. The problem is two-fold, first they lack deep context on the situation so land-up writing either off-base or just 'marketing' stuff about how they're the solution to the problem. It's not the candidates fault (or the job description) that the implications of assumptions will be wrong - it's just too early on.
Second, if I can't work out how their skills/expertise might be applicable to the actual problems I have (since I know the context), then I probably shouldn't be the hiring manager!
I read them because I recognise the effort that candidates are putting into creating them, and on occasion you get a clearer picture of the career arc behind the titles.
Where it may help more is for entry level roles where by the nature of the stage of career/life there's not much in a CV. In those circumstances providing some insight and background helps to clear the first hurdle, basically the "why would I spend an hour with you?" question.