It's not the same for telemetry. There's no way to verify none is transmitted, and difficult to intercept it or distinguish it from essential traffic. Not all telemetry goes to an HTTP endpoint. Some telemetry-like fingerprinting data can be gathered from basic requests (like an email provider scanning email headers, a phone app developer screening spam calls/numbers, a password manager storing domains of your accounts, and so on). More can be sent along with basic requests. And there is much more data/telemetry engineers could do if the number of users interfering with their methods became statistically significant.

I don't mean to fearmonger. I believe that most telemetry gathered is harmless to any particular user and is just used by data scientists and MBAs trying to see trends they can exploit in their business strategy. Ads probably have a much larger impact on an individual (emotional and mental effects), and there is value to ad-blocking services like Adguard. Still, apps claiming to block tracking, fingerprinting, and telemetry seem to target a very naive audience.