Sorry, what I meant by "Turn off route" is that you go a different direction accidentally (or on purpose)/miss your turn, or simply decide to go off the route (Turn off the road or highway) while Google Maps is giving you turn by turn directions to follow your pre-arranged route.
Or, in Google Maps - you can go off your route by pressing the microphone button, and speak your new destination while you are driving.
Turn-by-turn is your phone talking to you "In 200 feet, turn right..."
I use that a lot, and realize the route changes (there's your alternate, right there!) when I get caught up in traffic and miss the suggested turn.
I guess you never miss your turn!
I just do "Hey, Siri! Take me to work!" and follow Siri's instructions.
I don't do "anal-yzing routes" (see what I did there?)
But then, what is the use of studying the map before you go somewhere, when you have turn-by-turn directions.

Don't get me wrong on that, I pay attention to my surroundings, as I once had a turn through GPS that took me down a boat ramp
But, then I have to drive for most of an hour before I get into what I would call "urban/heavy" traffic.