I have a rather controversial opinion about them: From a purely personal perspective, I don't find them that important. I'm not particularly positive towards them. I'm not negative either, but I wouldn't miss them.
I have a lot of reservations about the 'right to be forgotten' on the internet and I don't think much of services that archive things without asking and by default (opt-out). I advocate for self-sovereignty, not for a service that undermines any efforts on my part as a website operator when I want to take something offline.
I know there is a robots.txt directive to prevent them from archiving everything. But, as I said, that's an opt-out, not an opt-in.
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