Hi orian and welcome to GE

First off I'd ask you to pay attention to the forum you post in. This one - Earth Browsing - is used for discoveries throughout our Globe. Questions like yours fit better another forum: Data Discussions.
So, please, help this Community to keep the place tidy!

All that said, let's talk about imagery now.

What Google Earth offers is a kind of mosaic made by pictures, taken by satellites and aircrafts, stitched toghether. Google purchases the rights of use of those images from different providers. Of course it's preferable to choose pictures without clouds for GE, at least when possible.

Also, when you find an area whose view is particularly clear, most likely it's covered by aerial pictures, like England (not everywhere though). Flying a plane costs money (a lot!) and I'm pretty sure companies that provide aerial imagery prefer to operate in good weather conditions as the results will be better and images will be easier to be sold.
Satellites take pictures continuosly, but, if cloudy images can be used for scientific purposes, those are not the best for an use like GE. Most of the sat pictures we see here come from DigitalGlobe. If you enable DG Layers you'll see that usually the clearest images are used on GE but they have "heavy Cloud Cover" imagery in their database too.

Now a question for you.
If you had to spend some money to buy pictures for GE, what kind of imagery would you prefer? Clear and sunny or cloudy and rainy?

Have fun with GE.
Bye
b