If I grotesquely oversimplify, on a street bike like paiggio which comes with a silent and a restricted muffler and plenty of "Jaliyan", bends and lengthy pipe, it pretty much comes down to providing the most silent gas flow possible to make it proper city commuter.
Furthermore, the its stock muffler is a EuroII complaint muffler which has a meaningful restriction to gas flow and harnessed with a emission controller,
So by changing to a low-restriction/free flow muffler and tailpipe on such bike gives a precious gain in low end torque. so simply any reduction in exhaust restriction is usually beneficial if and only if bike is also feeded with a free flow intake so I have removed one layer of foam stock air filter as well....
That my friend is a brake Oil bottle for rear brake!