About modes, they are tools like any other musical tool. For example, if you were to play jazz banjo…
… then knowing your modes and how to use them is nearly a requirement. And if you are to play tunes that step easily in and out of various keys from measure to measure, then the knowledge of modes is essential.
As for the Mixolydian mode, it is widely used to solo over V7 chords (Dominant 7th chords). As an example, in the bridge of the tune “I Got Rhythm”, the chord progression is D7, G7, C7, F7 resolving back to the key of Bb major. Over each “7” chord, you would play the corresponding Mixolydian scale (ie. D Mixolydian over D7, G Mixolydian over G7 and so on). In addition, the Mixolydian scale is a wonderful tool for playing over a static Dominant 7th chord in a funk or blues style.
So in this way, each of the modes has their own function in music. If you would like more information, I can send you a copy of the mode section of my book on the subject of modern music theory. It is written mostly for guitar, but the theory translates to any instrument. Just PM me.