Well according to our telemetry 0% of users turn it off so it seems pretty popular.
But more realistically what you gain in privacy you give up in having your voice heard by the devs. The decisions about the future of the product/project will be driven by the data, specifically the data from the kind of people who leave telemetry on.
See, I _am_ a dev. I run telemetry on my infrastructure, I analyse it and fix what's broken, and if necessary, try and get upstream fixed. Also, I'm not opposed to telemetry in general, but if a switch like this is turned on by default, trust is broken for good.
Software which does any type of computing without it's user's informed consent is classifiable as malware, mind you.
If 0% of your users disable it, that kind of screams there's something wrong with your opt-out mechanism. Is it broken? Hidden? Difficult to do?
I mean, with any group of people, there will always be a percentage that will disable it. If the telemetry is popular, that percentage might be very small, but it would be non-zero.
But more realistically what you gain in privacy you give up in having your voice heard by the devs. The decisions about the future of the product/project will be driven by the data, specifically the data from the kind of people who leave telemetry on.