If you mean that you have to restart an entire project, then it's not necessarily needed. You will need to create all maps from scratch though. Depending on how far you are in your project, it's something to consider. Though to up the quality, I'd recommend starting from scratch as that way you go into the project with a fresh mind and a new perspective, and are less likely to have any issues lying in wait. Also helps getting that new perspective as MV and MV3D is two different worlds :)