Sometimes selecting and using a manipulation is not very practical if you want to fine tune a model. Therefore you can just left click and drag any selected vertex. This feature also works with right button snapping. While dragging a single vertex you can press the middle mouse button to collapse the vertex with another vertex. This is useful for connecting two polygons or to collapse an edge.

While you are dragging around the vertex you can tap on the middle mouse button to increase the influence area and also move the vertexes around the one you are dragging.