Side imaging is good for finding brush piles and bream beds. It is not necessary to have it for long lining. The main thing with a fish finder is to find what depth they are at so you can plan on fishing above them. Fish will be scattered within a couple feet on the depth but most will be right around that area. With experience you will figure out what depth they are at. With regular long line trolling you don't even need electronics to catch fish. When I fish Greenwood I very seldom turn on my finders as I have fished it enough that I know what to start with and then go from there.