Patriots Strengths

Understand that the British pretty much kicked butt through the South. Some of the worst American defeats came in the Southern campaign. Also, understand that there was a very significant population of Loyalists (aka Tories) living in the South, fewer than what the British expected to find but stronger than Loyalists in the North. The British came South to energize the Loyalists, many who moved to Canada following the end of the war. In places, the Revolutionary War south of Virginia was closer to avicious civil war between irregular and militia units of Patriots and Loyalists rather than a set-piece action between British and Colonial regulars.

Still, here are the advantages---

First, the Patriots knew the landscape. The Swamp Fox, Francis Marion, for instance, made good use of his knowledge of South Carolina swamps to harass British troops in the area. 

Secondly, land. The South had a lot of land and few important cities. In the North, there was New York, Philadelphia and a number of other significant cities. The rural nature of the South allowed American generals Nathaneal Green and Daniel Morganto slowly withdraw north in front of the British troops, fighting a series of delaying battles. The British "won" each battle -- and would have won, IMO, even if Greene and Morgan were not using delaying tactics. 

However, the battles drew the British further away from their supply bases in Savannah and Charleston, while the Continental armies retreated closer to their supply lines. While the tactics used by Greene and Morgan minimized Continental losses, which could be easily replaced, British casualties were not easily replaced. And, the British inability to close with and destroy the American armies in the field frustrated the professional soldiers in the British army, sapping their morale as they marched north.

Thirdly, weather favored the Americans. Unlike the North, where winter was harsh, the South featured warmer weather. And for an army that had trouble with supplying winter clothing for its soldiers, this was a key advantage. 

Finally, the South was an agricultural region. This was before the invention of the cotton gin which turned the planters into cotton farmers. The Continentals retreated into an area where they could feed their army. By destroying supplies, the Continentals limited the British ability to live off the land.