Quote from IronMagus
Biomes are now grouped into "snowy," "cold," "medium/lush," and "dry/warm" varieties. Biomes of the same type tend to generate near each other, in large areas. So while in pre-1.7 Large Biomes you might have a great big desert, on a regular 1.7+ map you'd have a smaller desert, but next to that you'd have a mesa, then maybe another desert, then some savannah, and more deserts and mesas, etc., all grouped together. Altogether, it may be even bigger than just the desert was on Large Biomes. Now can you imagine if each of these were Large Biomes-sized biomes, and they were still all clumped together? You might not find an oak tree for miles!
Got it... so in essence Default became Large Biomes?