My understanding of Sketch is that it is an alternative to Photoshop for hi-fidelity designs.
I don't understand is how are people using Sketch as an efficient wireframing tool in the early prototype phase as an alternative to something like Axure or Balsamiq?
Sketch doesn't do nearly any of the advanced photo retouching stuff. It's mostly vector, mostly shapes. As flat UI gets more popular, sketch can increasingly do all the lifting on a hi-fi design, but depending on how crazy you get, photoshop is still king for that (anything involving texture, noise, pattern fills, etc has to be photoshop)
If you don't feel like learning a "real" workflow, balsamiq is quick because it comes with things like libraries of premade UI elements that you can just drop in without much of a learning curve.
If you're willing to learn sketch as a serious piece of software, it's very fast. Every design project I've worked on in the last 3 years or so has been 90% sketch. I drop back into photoshop for photo editing, or illustrator for advanced illustration (things with really complex paths or layer orders).
If you've got the interest, revisit sketch and try to put comparisons to photoshop out of your mind - sketch is UI first like photoshop is photo first, and it makes a big difference.
Once you get in the habit of building static sites as wireframe prototypes it's hard to go back to "wireframe only" tool.
Pop - iOS app. Draw on paper, take photos, mock up the page interaction. Nice for early demos. https://popapp.in/
If I have to show other people very early stage ideas I still use Balsamiq for the artificial lo-fi effect, but with other designers who have more control over their imaginations I'll just throw something together in Atomic.
Sketch is a more powerful tool (i use it most of the time now), but balsamiq is a great place to start.