What is the advantage of comparing mile splits (1st mile, 2nd mile...) in a MAF Test?

The advantage of comparing mile splits is that it tells you a lot about how much aerobic base you keep in reserve. In other words, the slope of your MAF speed between the earlier and later miles tell you how much aerobic endurance you have. A very steep slope tells you that you have very little endurance, while a slope of 0 (or nearly 0) for 12 or 13 miles means that it’s reasonable to suspect that your aerobic system is ready to run a marathon.

Someone who has been sedentary all their life may have a dramatic slope between their 1st and 2nd mile MAF Tests. This is because their aerobic systems are neither very powerful nor have a lot of endurance. A 21 year old, Division 1 5-k runner might have very fast MAF times for their initial miles, but observe somewhat of a drop-off towards later miles. For example, their first 8 miles might look something like this: 

1. 6'30"
2. 6'35" 
3. 6'30" 
4. 6'25" 
5. 6'30"
6. 6'55"
7. 7'45"
8. 7'55"

On the other hand, the MAF tests of a decent marathoner might go like this:

Miles 1-16: fluctuating between 8'35" - 8'20"

Miles 16-24: .3 min/mile drop every subsequent mile.