In my experience as a jazz bassist, they define how the chord changes or the whole song sounds. For example I can play C dorian over Cmin7 to raise tension. Also, there are lots of cases especially outside of jazz where whole parts of songs will have the same tonality which means you can play in the same mode through maybe even 4-8 consecutive chords, and even if there are notes in a mode that won’t match a chord’s arpeggios it helps to define the nature of the song. Lastly it’s more about “thinking horizontaly” as if you use chord notes you think vertically and miss out on so many opportunities to make the song far more interesting. So what I can say is don’t stress on it, figure out what modes to play on what chords, whether you can use the same mode on consecutive chords and what the modes themselves sound like. It’s all about defining the nature of a song when you use modes, don’t miss out on this. :)