As a bunch have noted already it really doesn't matter in some ways. In others it matters a lot.

If you're building a racing or high speed model you want the trailing edge to extend back to a razor like sharpness. A blunt trailing edge produces more drag than a razor sharp one. It may not matter as much in models as with full size but if you're racing where a single tenth of a second can be the difference between first and second then it pays to hone that trailing edge to where you can thin slice deli meat with your wing.

On aerobatic models there's no need. But if you round the trailing edge instead of leaving it sharp edged blunt then you increase the chance of inducing aileron flutter. And this is a very real danger even at our model sizes. The thicker and more blunt the more likely that it'll flutter if you round it instead of leaving it sharply squared off.