Surely "opt-in" destroys any validity the data would have (self selected groups are usually a poor proxy for typical users) even aside from the massive drop-off in participation.
Is there actually any data to back this up? Personally I see no reason why an opted-in group would be using an application that differently from the masses - your hot paths are still hot paths, common errors and annoyances will still be triggered. Really the only major thing I see that could be different is that a certain hard to find feature might be used more than it would otherwise.
But disregarding that, the argument is not "opt-in" vs "opt-out". Opt-out is not be on the table at all - silently collecting information from users without their consent or any affirmative action on their part is immoral, and damages user trust. So when you take that into account, the options are opt-in data vs no data whatsoever, and opt-in, taking into account any potential bias you think this data might have, is still more infinitely useful then getting nothing whatsoever.
If your issue is about the potential for deanonymization then that's understandable but that's a discussion where we would need to talk about specifics.
What I do alone in my own home should be known only to me.
Do I read books? It doesn't matter if I do nor what books.
Do I listen to music? It doesn't matter if I do nor what songs.
Do I watch tv? It doesn't matter if I do nor what videos.
Do I sleep? It doesn't matter if I do nor for how long.
Do I play games? It doesn't matter if I do nor which games.
Do I use a computer? It doesn't matter if I do nor what software.
What I do in my own home is private. Anyone looking at that without my explicit consent is violating my privacy. Usage patterns of what I do in my own home are immoral whether in aggregate or not.
We're talking about "What percentage of users clicked this button or used this audio filter?".
Recording what buttons I press is a violation of my privacy.
You also get (unless you are a contributor, I guess) a very capable and transparent music editing software for free.
For Belgium: https://www.bpost2.be/zipcodes/files/zipcodes_num_nl_new.htm...
Fun ones are 0612 (Saint Nicholas) or 1110 (NATO). We got great mileage out of 3 suisses until they went bankrupt.
Further random fact: The state and the postal services in Belgium don't always agree on the zip code. We found 1 location in Ghent where a monastery used to be, but it had been torn down and houses were built. The first inherited the address of the monastery, and hence had - on its own - a whole postal code, no street and no house number. But only for the postal services, not for the state (or the other way around, I dont remember). This location actually crashed the server for one geolocation provider.
Just to say, we are hackers, we're good at these games. They want a zip code? Find one for your country and feed it to them.
However telemetry reporting crashes with context information can be useful to identify bugs.
And the combination can be useful "each time a filter is being used it crashes" vs "the filter is used often, but crashes rarely"