Here's my attempt at an automatic window position recall macro. It only works for the front window of an app, but for me that's enough.
Save or un-save an app's front window position by triggering App Window Position - SAVE/REMOVE with:
⇧⌃⌥⌘W.
The next time you launch the app, this window position will be recalled for you. You can also manually trigger App Window Position - RECALL with:
⌃⌥⌘W.
Hey @noisneil, I’m looking forward to using this. My first observation when testing with Keyboard Maestro itself: when I launched Keyboard Maestro, it positioned the Variable Inspector Window instead of the Editor window.
That surprised me as I didn’t realize that window could be targeted by the Resize Window action. Perhaps adding logic to use the front window’s name as well could prevent this?
-Chris
Yeah that's the limitation, as I said. Front window only.
I'm up for exploring further but thought I'd share where I'm at so far.
Well apparently I have a reading comprehension problem today. 
The reason I haven't gone past "front window only" yet, is that it gets very complex very quickly when you start taking window names into account. It's fine for something like KM where the Editor's window name is constant, but browsers or text editors, not so much. So having one macro that can deal with both scenarios could be a bit tricky. Perhaps you could have a user selectable option to deal with this. Hmm....
Hmmm... I've realised there's additional complexity that I hadn't taken into account when it comes to screensets. I may have opened a can of worms...