do cases have to be trimmed after every firing? will it affect accuracy if i dont trim them?

no you don't have to trim after each firing.

Accuracy can be affected if the case gets too long. if its too long when you close the bolt you can pinch the case mouth against the chamber and the bullet, thereby raising pressures.

cases need to be trimmed when they get 10,000's over minimum length. if you only resize the case neck, i.e. "bump the shoulder" you won't create much stretch, abd won't have to trim too often.

on the flipside of that question, is there anything wrong with trimming them after each firing?

granted, they probably won't "need" it, but is there any reason not to, besides saving a step?