For the marathon in particular, as one poster already acknowledged, this can be a useful approach for running a type of specific intensity after accumulating fatigue.
This isn’t necessarily a workout focusing on marathon intensity but can serve as valuable training tool by doing a certain amount of “work” and then running a type of intensity specific to the race being prepared for.
It reminds me a bit of cycling long ride workouts where riders will accumulate “kilojoules” of work and then do a hard climb once they’re fatigued. In running it’s harder to try and gauge that type of energy expenditure.
I have athletes I work with do a similar sort of session for marathon prep, getting a specific type of exertion done like 5 miles warm up, 2 x 4 Miles at Marathon to slightly slower than marathon with 1 mile moderate between, then 2-3 x 1 Mile at Marathon Pace to slightly faster. Worth noting we’re also around 5k feet.
Another session I’ve had people do is longer warm up Then 2 sets of: 4mi @ Marathon, 4mi of :30 hard / 1:00 float. To be able to do specific types of quality responding to surges later in a race type environment.