From TFNA: “Stacking this [low intensity, long duration] workout on the back of the more intense one [the previous day] is thought to have the desirable effect of enhancing fat metabolism”

I’m looking for some more detail about the above quote – why does stacking benefit fat metabolism, and should we try to schedule our training to target this effect? e.g. do an easy Z1 run the day after doing a Muscular Endurance workout? Any references/pointers would be much appreciated. Thanks!