The key to answer this question, I think, is to understand the basic nature of authoritarian rule. While the news media focus on "the dictator", almost all authoritarian regimes are really coalitions involving a range of players with different resources, including incumbent politicians but also other elites like businessmen, bureaucrats, leaders of mass organizations like labor unions and political parties, and, of course, specialists in coercion like the military or the security forces. These elites are pivotal in deciding the fate of the regime and as long as they continue to ally themselves with the incumbent leadership, the regime is likely to remain stable. By contrast, when these elites split and some defect and decide to throw in their lot with the opposition, then the incumbents are in danger.
So where do protests come in? The problem is that in authoritarian regimes there are few sources of reliable information that can help these pivotal elites decide whom to back. Restrictions on media freedom and civil and political rights limit the amount and quality of information that is available on both the incumbents and the opposition. Moreover, the powerful incentives to pay lip service to incumbent rulers make it hard to know what to make of what information there is. Rumor and innuendo thus play a huge role in all authoritarian regimes.
In this context, protests are excellent opportunities for communication.
(Photo: A Libyan protester steps on a poster of Libyan Leader Moammar Gadhafi during a protest in front of the Libyan embassy in Cairo, Egypt, Monday Feb. 21, 2011. By Hussein Malla/AP)