I started implementing them (I use 60 seconds on, 30 seconds off) to increase my work at slightly faster paces, mostly for running economy purposes. I've been racing faster than before with this method, but I've also gotten a tad more sore after races (or workouts I jump in to pace friends) so figured a bit of muscular conditioning would help. I've found the faster reps have made me feel "snappier" all around. Introducing them and finding the right paces, however, was a bit tough bc you can really only dial in on effort (RPE) and pace to find the just-under-threshold sweet spot. Because of that, I wonder if people leave them out just to avoid overcooking themselves. I also haven't been calculating TSS and CTL but I wonder how it compares versus, say, 10x3 min.