Since humans first developed stable agriculture, seeds have become the world's most essential crop. That's because seed is the bridge between one generation of plant and the next.
There isn't a single good reason for planting poor quality seed, and, thank goodness, this is one thing you can control. The general rule is the larger the seed for any particular variety, the stronger and more vigorous the seedlings are likely to be. Large seeds also produce plants with more tillers than those grown from small seeds.