I have a Lowrance unit and added the side scan/down scan equipment. I've found the important thing to keep in mind with the side scan is you need to be moving in a straight line and need to be moving at a certain speed. Not too fast but you need to be moving some. Inshore.... awesome. Offshore I havn't used it much becuase of the conditions I've mentioned and add in the swell, etc. I wasn't getting a good image when I tried. That said if I really wanted to get a better image no doubt I could do a few more passes and get darn good image out of it but I never bother. When that 2D sonar lights up I'm ready to roll. Straight line movement is critical to getting good images. If I farted around with it I'm sure I could see some really cool stuff but I'm usually just trying to mark fish and bottom on the 2D and get setup so I can start fishing. IMO the 2D marks fish much better than the side scan/bottom scan, I can watch a 4oz lead sink to the bottom. The fish mark differently on the side scan and its a little hard to decipher if your used to seeing 2D sonar arches. I don't know what shrimp look like on it because I have not tried it for that.

I've seen some awesome stuff with it! Have I parlayed that into catching more fish...not necessarily. Typically I'm going over areas I know well (just to see whats there) but I do have a better understanding of what I've been fishing and I've found some cool stuff that I've yet to come back and fish. I don't think its giving me any advantage in that respect, if you can't catch fish now the side scan isn't any mirical machine.  

My 2 cents.
Inshore=Awesome
Offshore=Not really needed
freshwater... never used it in freshwater
For identifying bottom its great, for marking fish in the water column 2D is better.

I like my Lowrance and people feel equally as strong about their Humminbird units. I did lots of research and am happy with my decision.