Purpose of a Particular Workout

I’ve seen it posted many times workouts like:

1x300 @ 95%, wait 60 sec. then 4x60 w/walk back rest

What is the purpose of workouts like this where you run all out for a long distance (Special Endurance), then do some sort of rapid-fire speed endurance work (4x60)? What time of year do you use these? Thanks.