Lake map contours are helpful if/when you're wanting to stay in a certain depth or work over a flat. It's just a broader view of the whole area of the lake you're on. The only downside I can see is that it takes up a good portion of your screen when being used. (which is probably why you see some boats with two or three units at the bow &/or the console)
I'll find out for myself this year, as I have a map chip in my Hook 7 (first time for me having a map chip)