Advantages:
From a conservative or state-based ideology: it is much easier to control population since they rarely receive "strange" ideas or influence from outside. Domestic policies become much more important. In so, it becomes easier to set popular aims targeting citizens.
The country could(historically seen) stand the best defense against outside powers which could try to set an invasion. For example, the Great Wall of China turned out to set a strong defense against Mongols and other menaces along many centuries.
Disadvantages are listed:
Trading with other countries can influence negatively on economic growth, as there is no autonomous country even if it results as big as China.
Trade has become key in today's globalized world, henceforth the need to collaborate or cooperate in economic exchanges is a necessity to keep up the pace in global affairs.
