The two tools Convert to Erase ALL Existing Paths and Convert to Erase NO Existing Paths both operate on an Erase Path (a path where at least one of the paint layers is erasing) and alter its erasing behavior. If the option Erasure Honors Creation Time is turned on, an Erase Path can only cut through those paths that are both below it (see Z Levels) and were created before the erase path was created. This allows you to create paths after an erase path has been constructed and then move them beneath the erase path using one of the z-level manipulation tools. The path will be visible through the hole created by the erase path. The Convert to Erase ALL Existing Paths tool changes this behavior so that the erase path cuts through all paths below it regardless of whether they were created before the erase path or not. The Convert to Erase NO Existing Paths essentially converts the erasing layers of the path to simple transparency. Note that because of this, if the entire path is erasing (as opposed to only a layer of the path) then the entire path will appear invisible. If the path is only partially erasing (for instance, only the middle layer paint is erasing) then no paths below the path will be erased and they will all show through the hole in the erase path. Here’s an example: