When I learnt about gas flow it was taught to me that a certain amount of back pressure helps to improve the flow of aireated fuel into the cylinders and the removal of exhaust gases afterwards. Its something to do with vortexes, and how they affect the movement of air/gases in a enclosed environment. I worked as a Air conditioning unit builder for a few years, and had to travel to a massive IBM facility near Portsmouth (Havant) to help fix a flaw in the sub-contractors installation of the units I built. They used the wrong sized ducting to spread the cooled air throughout the facility, so the air just wasn't moving. It was cheaper to modify the AC units than to change the ducting, so I spent three weeks atop a cherry picker, ( bloody high up as well) changing fans and their surrounds to create back pressure and get the system working properly.
On the same track, I have a 250 that has a balancer pipe joining two equal length exhaust pipes on a twin cylinder engine, and due to its position it gets covered in crud and rusts badly, so I tried two unconnected exhausts and the bike would not run properly, especially at low revs, so had to revert back to a linked system. A twin with equal length pipes should not need a balance tube unless there is a issue with the exhaust gases expulsion from the cylinders