They have a switch to turn this off, but then they say this:

> The nitty gritty: when you turn the flag off, the events are sent, but we tell our servers to not store these events. They're dropped immediately — they're not stored or processed at all. The reason that we chose to do it this way is so that when you turn it off on your desktop app it also turns off automatically on your phone - and vice-versa. This allows us to keep things the same across all of our apps and clients, across upgrades.

Why not do it both on the client and server...

Because the network itself is also listening and never forgets: https://en.wikipedia.org/wiki/Utah_Data_Center