[Traps]

Get more information about going to failure here

So why go to failure? Let's say you're using a load of 70% of 1RM and the target muscles have a similar threshold for total MU recruitment and exhaustion. By reaching concentric failure, you've recruited and exhausted all FT MUs. However, beyond 80%, the load is great enough to do this to all muscles without reaching failure. Going to failure at this point is now like pushing the engine of your car to redline and not shifting gears. You're subjecting the CNS to unnecessary fatigue. You've recruited all fibers so what is your goal now? To try and further exhaust the CNS? Why?
I'll quote Zatsiorsky again: "...a trainee should “learn” to either decrease inhibitory output or enhance excitatory output from the central nervous system (CNS) while exercising and thereby gain strength. This learning is more successful if the trainee is fully recovered from the previous activity, not fatigued."
Going to failure induces greater fatigue. With heavier loads this is even more pronounced and not only interferes with rest times between sets but can have a cumulative effect that affects workout scheduling (consider many HIT trainees who train once a week). So why do it if you're using a load that recruits and exhausts all FT motor units without going to failure? What does it achieve other than induce unnecessary fatigue? The facts are all there.