Hi Dan, in my limited experience I've used for both. In some ways it was very flat designed oriented from a beginners perceptive.
If needing graphical textures (you can do some basics in sketch) or things deep etched then these need to be prepared before hand and then brought into sketch. Generally feeling is that you need to be more planned when using Sketch, which may suit some users to a tea.
It was great for wireframes.
For the time being I will go between the two depending upon the design nature of the site.