You can use it to watch every process send network traffic, you can even collect samples of the traffic and plot it on a map: https://www.obdev.at/products/littlesnitch/index.html
(not affiliated, just a happy customer; it's one of the few things I like the mac ecosystem for.. there's attempts to port it to linux with https://github.com/evilsocket/opensnitch; but it's not as polished of course)
Concerning.
Thank you for fixing it, I can't edit the post now.
That happens whether or not you are logged into icloud/facetime/messages at the same time, or not.
Anyone aware of a way to figure out what nsurlesssiond is downloading/uploading in the background?
The desktop appeared, and the system was connected to a dedicated wi-fi network for the purpose, DeviceUnderTest. 60 seconds or so of “no activity” simply staring at the desktop elapsed, and the system was rebooted, automatically reconnecting to the test network.
Wi-Fi was then disabled.
...
In this few minutes, the system generated 38 megabytes of network traffic.Note: this anecdote may no longer be current. I’m not sure what changes Apple might have made since I tested this.