Using the "Layer Brush" for carving patterns into objects as done by @theluthier with the "CG Cookie" logo and a "Jack O'Lantern" is quite useful. However this brush doesn't work properly in Blender 2.90+ with the "Persistent Base" setting that allows you to exclude areas from getting a new mesh layer where you've already painted since the last time that you've pressed the "Set Persistent Base" button. This works fine after hitting that button for the first time but when you press the "Set Persistent Base" button for a second time Blender 2.90+ doesn't save that mesh state as new basis. For making it work, you have to tab into "Edit Mode" and then back to "Sculpt Mode" before pressing the "Set Persistent Base" button again. The same problem shows up when switching to "Local Mode" or choosing another object as reported here. In Blender 2.83, everything was working as intended so that I suppose that this problem was introduced with the transition to Blender 2.90 where it already exists in the Alpha version.