Why TDM needs your PRECISE location
Navigation lives on your exact position. TDM uses it to keep the map under your vehicle, to tell which junction and which lane you are approaching, and to trigger every announcement at the right moment - 'turn right in 200 m' only works if 200 m really is 200 m. 'Approximate' location is not enough: it is accurate to a few hundred metres, and with it the map freezes, no announcements are spoken and nothing is recalculated after a missed turn - exactly what we saw on our field test. So when Android asks, please choose 'Precise' and 'While using the app'. Your position stays on the device - TDM does not send it anywhere.
See also: Why TDM needs the notification permission · Without both permissions there is no navigation
Why TDM needs the notification permission
While you navigate or record a track, TDM runs as a foreground service - the part of the app Android keeps alive when the screen goes dark or another app comes to the front. Android only allows such a service if it may show a notification. Without the permission the system shuts the service down: announcements fall silent, the recording breaks off, and on Android Auto the guidance on the car screen stops in the middle of the route. The notification is nothing more than the 'Navigation running' entry in the status bar; TDM sends no advertising and no other messages.
See also: Why TDM needs your PRECISE location · Without both permissions there is no navigation · Android Auto
Without both permissions there is no navigation
This is deliberate: as long as precise location or notifications are missing, TDM does not start navigation at all - neither on the phone nor through Android Auto. A navigation that silently cannot guide you is worse than a clear no, because you only notice once you are already on the road. If a start is refused, TDM tells you which permission is missing and takes you straight to the right dialog. Denied for good ('Don't ask again')? Then the button leads to the system settings, where you can grant both in a few seconds. Everything else in TDM - planning, maps, passes, POIs, this tour - works without them too.
See also: Why TDM needs your PRECISE location · Why TDM needs the notification permission · Android Auto