Use it to communicate that progress is satisfactory up to the current point in time. Our road trip has been relaxing—so far, so good.
Pro Tip 2/3
Cautious Optimism
It expresses cautious optimism about the future, acknowledging that the current situation is okay. I've only seen the trailer for the film, but so far, so good.
Pro Tip 3/3
Not Overconfident
It suggests that there's more to come, and the outcome is not yet certain. The surgery is going well, so far, so good.