On the track, you're going to make lots of trips around each turn and can establish turn points that are reliable and meet all of the objectives you have for the turn. They serve the purpose of letting you concentrate on other things (like entry speed) on the approach to the corner, they give you a place to turn the bike that serves to place you onto your preferred line and they tend to facilitate getting the bike turned quickly (as opposed to groping your way into the corner) so you can get back to the gas.
Yup, they're quite valuable on the track where you're going round and round the same set of turns, but I never use the concept on the street because I never know what's ahead. I'm scanning my vision between close and far, looking for gravel or potholes and then looking up to see where the road goes - and even on a very familiar road, the conditions might have changed since I last rode it so I can't trust that whatever turning point I used last time is still safe. And, I don't care about entry speed, and I need to maintain enough margin to safely change lines at any point during the turn. For all these reasons, I've never found the concept to be useful on the street, though if others do then that's perfectly fine.