Who doesn't like wall plates?
They will not affect the sound if you make a good secure connection and you will if you use decent quality jacks and plates like the ones from PE.
They are mainly for convenience to hide wire. As far as other solutions, sure you can just use a 'pass thru' plate which is nothing more than a wall plate with a giant hole in it through which you pass all wires. That's not very clean looking but will certainly work.