Cross over is used to let the gases of a cylinder have more way of escapement.
Thats good if the mufflers have a restrictive baffle.
With an open muffler theorically the cross over is no more needed.
Removing the crossover has been an estetical issue for Harley owners with that ugly pipe in front of the cylinders (early big twins and Sporty).
But if you remove the cross over with still restrictive baffles there's a small loose in torque and power and some more vibrations.
The sound of course get better without cross over because the two exhaust notes don't mix.
With a cross over the exhaust gases of a cylinder that is in exhaust phase go out from that cylinder's main pipe but with a short retard due to the smaller diameter of the cross over tube, from the other pipe too.
The sound of every exhaust phase become a bit mixed.
Without cross over every exhaust phase note is more distinct.
Harley owners know better about it. And it's an important issue for them.
