One thing to note is that you don't have to always play a note at the same frequency, even in the same piece.

On the violin, it's common to adjust intonation to different concerns: to bring out multiple voices, to put emphasis on the melodic line, or to nail the chords.

I don't know how hard it would be to do this digitally though. I imagine it would be quite tedious to work on a fretless digital music software.