I have an Leaflet map with a TMS layer. For each zoom change, my map makes about 20-50 requests for map tiles (depending on the map/zoom/screen size). If the user rapidly zooms in or out, all these map tile requests get queued up. Even if zoom is not visible, all it's tiles will be loaded. It is possible to configure Leaflet to cancel ajax request for invisible tiles, like openlayers does.