It shouldn't matter but often it does.

1. Traditionally, the quick release lever goes on the left.
2. Some tires have a direction of rotation arrow on the sidewall. Frankly, I don't think that it makes much difference on a mountain bike and I doubt it makes any difference at all on a road bike.
3. Here's the biggie: If your front wheel isn't dished perfectly, your brake can rub if the wheel is installed backward. I know that shouldn't happen, but in real life it's common.