Most people would want to at least have 2D sonar up front. If trying to position on a drop or over a brush pile it is good to not have depth coming from a boat lenght away.
It is interesting that on BBG Marine's web page the G2 DI unit is actually less expensive than the G2 2D only unit.
http://bbgmarine.com/index.php?main_...nbird+helix+10 .... although the Mega DI unit is quite a bit more. I actually didn't realize there was a mega DI unit and a non Mega DI unit in the G2N series before doing that search.