Balanced leeches are a terrific innovation on a common streamer pattern. They are designed to suspend the fly horizontally under a strike indicator, positioned like a real minnow or bait fish. Regular streamers must be continually stripped to maintain a horizontal position - if stripping is stopped they sink to the bottom or drift in an unnatural orientation. This patterns works very well in lakes and ponds and we have had great success using them in rivers, especially in slower, deep pools and runs. Tied on a size 10 hook.
TIP: Try using balanced balanced as the bottom fly of a two fly rig with an Ice Cream Cone above it. If possible, use a non-slip loop knot to tie on the leech - it will allow more movement of the fly in the water.