An advantage would be that it allows the majority to pull themselves out of a dictatorship or other bad situation. Like how the American colonies fought against the British to gain their independence because they felt they were being taken advantage of and not given the respect due to them ("no taxation without representation").
A disadvantage would be that it could put the wrong people into power (like a heavily armed and trained extremist group). It could also destabilize the country, harming the economy and tourism, and making the country more vulnerable to armed revolts in the future. It could also be unnecessarily violent and kill many innocents in the process; one good example of this is the French Revolution.
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