Hi there,
not all themes work the same. Most stock themes use inline styles to handle user customization, meaning that each and every page contain the whole CSS in the header, making pages heavier.

Stoked! actually regenerates a new external .css file with your customization. This is faster and allows caching by browsers. The downside, as you noticed, is that you might have to clear your cache to see changes, but overall you'll get better performance (which I personally consider more important).

Hope it helps