I think the difference is between free patterns and for sale patterns by one company/person. If they're both offered by the same company or person, the free patterns are generally not as detailed, or they took less work to produce. However, there are lots and lots of simply wonderful free patterns out there by many different people and companies. I buy patterns regularly, because if there's a pattern for sale that I just love
, I'm more than happy to pay for it. But I also use free patterns just as often.