What baddox says is true, but I have to add that there is a noticeable difference in timbre between the same note played at two different places. So if you find yourself with the choice, you have to use your own judgment to decide which fingering you think sounds better.

Yeah, it's mostly about playability. It's easy to get into a position where you're playing the notes in the current chord correctly, but there's no way to play the melody of shift elegantly to the next chord. Classical guitar sheet music contains a lot of hints for fingering. Fret bar indicators are quite common, and sometimes you'll see complete stacked fingering indicators. Some more difficult pieces will give you almost nothing, and it's up to your experience (and just brute force) to figure out the ideal fingerings.