Fair lords, said Sir Ironside, I cannot tell you, for it is full hard to find him; for such young knights as he is one, when they be in their adventures be never abiding in no place.
Sir Thomas Malory, Le Morte D’Arthur
Two-sided printing is great1. I like using both sides of a page or card.
But nobody likes a sheet that you have to keep flipping back and forth to reference information (or to apply information that’s on one side but refers to some stat or numbers on the other side, so you have to flip to the rule, then back to find the data, then back again).
Ideally, you only ever use one side of a reference sheet at a time - flipping it happens when gameplay or the answers you’re looking for switch into a different mode of sorts. We can put an end-of-year summary on the back of the character sheet, for instance, because you’re using it at the end of a session when you don’t need all the main details.
Most of the time this means there’s one side of the page which will be used more often - which is okay. Oftentimes, this means the other side of the page is a cemetery, there for details you want when there’s no need for the other side any more.