If you have a wide Chest & Traps the chest straps really help
I really don't understand this. If you have a wide chest, the slots on the top of the backplate will tend to hold the harness straps in so that they ride nicely in the hollow over your collarbone. No need for a chest strap at all. It's those of us who are very narrow who have problems, because the harness straps going from the slots at the top of the plate to the ones at the bottom ride over the ball of the head of the humerus. This causes them to want to slide off the shoulders, and also cut into the inner upper arm. That's where the crossed straps are helpful.