I only played with it for about two days, as I don't really have a need for a drawing program, but from my experience, and I hate to be a Google nerd, and I'm no pundit, but Google's stuff works..
Threads will be a good learning experience I think, I never got that far because it's one of the procedural functions of Sketch, you'll get as much out of this software as you put into it, and when you hit your limit the commercial version will probably be the next step.
The free version is powerful, and the pay version contains what is required for more commercial applications, and it's not ungodly expensive.