Why should I use a burr grinder instead of a blade grinder?

Burr grinders produce uniform particle sizes, which means even extraction and balanced flavor. Blade grinders chop randomly, creating a mix of dust and boulders that leads to simultaneous over-extraction (bitterness) and under-extraction (sourness). Even a $50 burr grinder like the Baratza Encore dramatically improves cup quality over any blade grinder.