Then select other vertices (ideally on the same mesh, but it can be other mesh, just make sure you have the same influence on it) and press Ctrl + Alt + v.
Pretty usefull for putting your desired influence weight mix to other vertex selection, which would otherwise be quite difficult. It is also a way of making certain part of the skin look rigid. Like big scales of the dragon or to maintain clothes edges together.
This website contains this shortcut and also many others you might find useful:
If you are interested further, it is using a function in a script MAYA_FOLDER/scripts/others/findSkinClusterFromSelectedComponent.mel