Once a build is done, the use of a wideband to make sure everything is working right and the tune is reasonable should always be used. What a wideband can not tell you is how much boost is safe or reasonable for your set up. You can normally never run the edge safely, because you need room for safety if the fuel or conditions are less than ideal. The J&S unit lets you know how safe your set up is and can adjust the timing down to keep things safe if conditions or fuel change. The J&S unit allows you to run the edge because if you go over the edge, it backs you down. Detonation does not instantly kill your motor unless it is crazy hard detonation. Mild detonation slowly eats your bearings and can fracture the pistons. The motor can let go just doing a casual drive because the damage slowly ate the engine over time and when it fails is not always when your driving hard. Many people are running too much boost and do not realize they are detonating regularly. Many engine builds have higher compression than stock because the pistons are higher compression with out them knowing or from the heads being surfaced and engine blocks being decked. Higher compression causes the need to run less boost to not detonate. The correct air fuel ratio is important, but timing,boost,compression are all part of what is safe for a given octane. The ability for something to monitor knock and pull timing if anything is not safe is HUGE.
