1. There's Less Competition:
As the weather get cooler, people are more likely to stay indoors. This allows serious buyers to get what they really want at the price they really want because they have better bargaining power.
2. Sellers are more motivated to sell:
Most sellers expect to sell during peak season (summer time). If they're not able to sell during that season, they are even more motivated to see during fall. The buy has better bargaining power.
3. You can take advantage of tax breaks:
Even if you close on your house in December, property taxes and mortgage interest are deductions you can take for your whole years worth of income.