The need for downthrust plays hand in hand with the CG position and final elevator trim. Dan up above is getting away with the 0-0-0 setup because he's comfortable with his models flying like precision aerobatic models. Nothing wrong with that at all if you're an attentive pilot and don't mind making your own minor corrections. But most folks will set up sport and scale models with a whiff of positive decalage (wing to tail angle) and a slightly forward CG to get SOME degree of trimmed in pitch stability. And when you do that you may find you want a touch of down thrust.
Side thrust is another puppy. It does pay to use a degree to degree and a half of right thrust to aid in counteracting torque on takeoff and during climbing.
Full size aircraft often use some slight fin offset on the old big engine prop planes. But our models do not have the same issues with prop to wingspan ratio as the heavily powered old fighters and some trainers had. So we are fine with the fin and rudder being centered.