I do my best to maintain online anonymity for two primary reasons: one, it lets me actually engage in real conversations with people rather than having to be selective about how and what I can talk with people about. Two, it helps with evading surveillance (particularly marketing surveillance) by keeping a firewall between my online personae and my real life.
There's a third part, too, related to telemetry -- if I know that telemetry is being collected, it changes how I use whatever the thing is because I have to keep in mind that my interactions with the thing will affect iterations of that thing. Let's take YouTube as an example: knowing that my watching habits are being recorded means that there are times when I'll play a video or let it run to the end even when I'm not interested in it at the moment, because I don't want anyone to draw the conclusion that I'm not interested in it overall.
There's a third part, too, related to telemetry -- if I know that telemetry is being collected, it changes how I use whatever the thing is because I have to keep in mind that my interactions with the thing will affect iterations of that thing. Let's take YouTube as an example: knowing that my watching habits are being recorded means that there are times when I'll play a video or let it run to the end even when I'm not interested in it at the moment, because I don't want anyone to draw the conclusion that I'm not interested in it overall.