I use a graph most of the year to help me catch fish. Every season is different, so I will discuss each season separately.
In the winter, the fish bunch up good in the cold water lakes. They are fairly easy to find, but hard to catch (or distinguish the species) unless you use finesse presentations and fish almost motionless. It is tough to make a lure look alive when everything in the lake is dormant. So, you can't fish like you can in other seasons.
I often use my graph (side-imaging especially) to find grass in the shallows and fish for aggressive fish that move shallow to feed. I usually catch bigger fish shallow than deep in the winter.
In early spring, I like to use my electronics to find channel bends in the shallow coves after we've had a warming trend. I also use my graph in early spring to get the water temp. But other than that, spring is not a time I use my electronics much. Once the spawning process begins, most of the fish are shallow and I am there with them. I prefer to look for huge bedding fish with my eyes and my graph is no help. I am bad about tearing up my transducers in the spring. I usually take them off during the spawn (if a tree doesn't do it first).
Summer is a good time for using a graph. I use it to find fish, humps, grass, and the thermocline. Fish will be on and off the humps during the day when they are feeding on shad and barfish. Keep checking the deep humps and occasionally they will be loaded with bass. However, more often than not, they aren't actively feeding. During the day, most of the fish will be inactively suspended in the thermocline. That is the best place to fish if you must fish during the day. The problem is that since the fish are inactive most of the time, it is hard to be consistent. I hate to waste my clients' time idling around looking for fish that are active. The only guarantee is that you won't catch anything until you quit looking and start fishing. So, I don't spend a whole lot of time looking if I don't find fish quick. I prefer to use my graph to find the grass edges and come around at dark and take advantage of feeding bass lurking around the grass. Night fishing is awesome in the summer.
Fall is absolutely the best time to use a graph. The thermocline is gone, so most of the fish are relating to the bottom. The water is still warm, so the fish are active. The lake isn't heavily pressured. And, best of all, the bass are easy to locate and get to bite. If you want to learn how to use a graph to find and catch deep water fish, do it in the fall.