Wether you are sculpting or painting in any application, symmetry offers a way to work on one side, while affecting both sides of you model. Most applications use symmetry based on a tolerance or similarity between the two halves. ZBrush works similar, but Zbrush will allow you to use symmetry on both symmetrical and non-symmetrical shapes, with non-planar symmetry.
If you don’t have a perfectly symmetrical model in ZBrush, but still want to work with symmetry enabled, non-planar symmetry is the way to go. Here, Arrimus 3D shows how you can employ non-planar symmetry in ZBrush, allowing you to work with any shaped object.
Arrimus 3D creates quite a few tutorials ranging in various subjects. If you enjoy or make use of his tutorials, Arrimus 3D has a Patreon page, where you can donate. Check out Arrimus 3D on Patreon here, and consider donating.