u/RealBlad

So what is exactly the difference in meaning/nuance between these two?

To me it seems you can't swap ulkona for ulkosalla in sentences like this:

>Ulkona oli pari kulunutta pöytää

But in sentences like these you can always swap ulkosalla for ulkona right?

>Vanha mies valmisti kalaa ulkosalla

>Monet seisoskelivat vielä ympäriinsä, tervehtivät toisiaan ja jutustelivat ulkosalla

So what would be the difference if you were to use ulkona there?

For other words in general as well, what would be the difference in using the -sa- form over just a single location case? E.g. kotosalla and taivasalla