Our take
This 30-second clip from Vilius Schulte tackles a stance fault he says he sees all the time: feet too close together and the body turned too far side-on to the shot.
He gives two reasons why it matters. A narrow base makes you unstable from side to side, and, depending on your build, being too side-on can leave the back arm without room to swing freely. If that happens the cue tends to wander off the shot line through the delivery and your finishing position suffers.
His remedy is refreshingly simple: widen the gap between your feet so the body has room to stay balanced and the arm can move without obstruction. Importantly, he is not saying side-on is wrong in itself; plenty of good players use it. It is a matter of finding the position that suits your body. Try a few stance widths on a straight pot and see which keeps the cue straightest.