Freesync is useful for when you can't achieve a decent minimum framerate for example, since it's variable it looks good even when you dip into the 30s and 40s for a few moments or during action sequences because otherwise monitors lock down on set intervals like 30 then 50 then 60, etc. (Depends on the monitor) So if you drop down to 45 FPS then the monitor locks refresh rate at 30 FPS making it very noticeable whereas Freesync can do 45 refresh rate and vary according to what the game is pushing out.
It's always better to have a card that might not need to use Freesync or Gsync since it can maintain 60 FPS minimum at all times so your game will look fairly smooth even if you are not using vsync.
An overall higher refresh rate with higher minimums is better than variable refresh rate imo. The 1070 is substantially stronger and can maintain these 60 FPS minimum at all times on fairly high or even ultra settings for 1080p and even 1440p whereas the 580 will maintain 60 average but with more frequent slowdowns.
sAnr0 reacted to Misanthrope in Rx580 or 1070