[kruczek]

Well, if you use it only for their messenger, then they can still for example track webpages you visit (either via cookies or some finer fingerprinting based on e.g. user agent).

It may also be a bit of a knee-jerk reaction, but in a world where even seemingly innocuous data is used to find unexpected correlations and identify people, I certainly prefer to keep a safe margin of error and steer away from companies which live on our data.