When fishing with sinking lines it is often very important to be able to raise your line to the surface prior to delivering the cast of your choice (see picture below). This effectively affords you a brief window in which to you are able to treat your sinking line in the same manner as you would your floating line, therefore making it much more manageable whilst casting and allowing you to enjoy your fishing experience much more.
One of the advantages of fishing with a sunk line is that it enables you to present your fly at the fishes level, at any depth in the water you may require, but you must first take into consideration the sink rate of the line you are using and the speed of flow and depth of water you are fishing. Weight of fly, leader length and diameter will all have a bearing on how efficiently you are both casting and fishing.
One of the disadvantages can be the fact that once your sunk line has been cast out onto the water, the opportunity to introduce a mend to to your fly line, to either speed up or slow down your fly has often gone, due to the fact that your line is now sinking. This can be overcome by the introduction of an ariel Curve or Mend, during or immediately after the forward stroke/cast. See relevant links on Curves & Mends. Many sunk lines now have a floating running line to assist with this problem.
"In general, the darker the line colour, the faster it will sink".