Cucumbers have a lot of water in them. When you dress them, the salt in the dressing will leach out some of this moisture, resulting in a lot of excess liquid. One way to get around this is to salt the cucumbers first, let them sit for a while for the salt to work its magic, then rinse off the salt and drain the cucumbers. This is step one in this recipe. You can skip it if you don't have time, but the result will then be much more watery.