Every species of fish has a preferred water temperature range. Think of water temperature as fish holding structure. Using preferred water temperature as your guide, it is possible to eliminate a lot of un-productive water quickly. Fish want to be where they are comfortable, so it pays to fish in their preferred water temperature range!
Every body of water has temperature changes from the surface to the bottom. There are layers of water where the temperature will be significantly different from the surrounding water. These differences are called "temperature breaks" or the thermocline. Larger, deeper lakes tend to have more temperature breaks.
When fish suspend in the water column it is usually by water temperature. Using a temperature probe will allow you to find the depth of the correct water temperature for the species you are targeting. Using the Fish Hawk Probe on your downrigger, lower the probe close to the bottom, observing the water temperature on the display as you raise the probe to the surface. Or using the Fish Hawk TD, simply attach the TD to a fishing line or the downrigger cable and lower it to the bottom. When you retrieve the TD, press the "VIEW" button and it will show you the water temperature every five-feet.