NT SERVICE\SQLTELEMETRY User I've noticed that SQL Server 2016 installations include a new default login called NT SERVICE\SQLTELEMETRY. I'm aware that for the free editions of SQL Server 2016 you agree in the license to allow your server to send telemetry information to Microsoft. I would guess that this login is associated with that work. As part of our new instance installation process we prefer to clean up and remove any unused system or default logins to avoid potential holes in security or clutter. Does this account do anything particularly important such that we'd want to keep it and if not would it break the license agreement to disable or delete it? I should note that our SQL Servers are generally not Internet facing.
This login is used for Extended Events. More information here: Extended Events logins

I disabled it once, and I was no longer able to collect the data I needed. If I were you I'd keep the login as it is, unless of course you already know that you wont need tracing/Extended Events.

When it comes to telemetry you may like to read the instructions how it can be disabled: Disable telemetry Apparently many users are not happy about telemetry. More information here