Sunshine and daylight are the key ingredients to making your space feel beautiful, when I'm working on a new project the orientation of the site is the first thing I will look at - everything else is determined by that. You do not want to build a large extension which is dark or feels cold most of the time, sunlight makes us happy so we try to bring it in wherever we can. You also don't want to create a bright extension which then leaves the rest of the house feeling darker!

On a side note, the glass box architecture takes this to an extreme which I disagree with - there is no point creating a space that needs blinds down all the time to feel comfortable - it's all about balance.