Depends on where you are and if your airfield has an instrument approach or letdown procedure (and your aircraft is equipped to fly them). Some of the best conditions for teaching the early exercises can be found on top of cloud with a perfect horizon and smooth air, added to which it is sometimes beneficial to be able to fly through some crap to get to an area of clear weather with some confidence. Again, depends on where you are - some areas suffer more than others from that sort of weather. The other advantage is that you will be much more conversant with radio nav so can use beacons to keep tabs of where you are during some of the more protracted lessons - it's sometimes easy to forget if you're really getting into teaching something and it's all falling into place for the student!