Because of the shunning of Boycott, the practice of not doing business with someone because you didn't like their politics first got its name, although the practice had existed before Boycott himself was, er, boycotted. Some three centuries later, boycotts are more popular than ever, thanks in part to the Internet and to the tendency of some people to jump on whatever bandwagon comes along.
Historically, boycotts have proven to be an effective means of economic coercion. The Montgomery Bus Boycott is one example of people deciding that they didn't need to pay their hard-earned money just to be mistreated. By the way, I expect anyone who wants to know more about the Irish Land War or the Montgomery Bus Boycott has the ability to Google those topics.
More recently, though, boycotts have seemed to be more about calling attention to a perceived offense, rather than actually affecting social change. You may remember that President Jimmy Carter had the U.S. boycott the 1980 Olympics in Moscow because the Soviet Union had invaded Afghanistan. Four years later, the Soviets returned the favor by refusing to send Olympians to Los Angeles.
Neither of those boycotts did anything to affect foreign policy. They accomplished nothing other than hurting those athletes who had trained for years to participate in a competition that they were barred from. In the 21st century, most boycotts have devolved from noble causes into essentially personal vendettas against individuals.
The most egregious example of this is when a group decides that they don't like a particular TV or radio show. Rather than doing something radical like changing the channel, they contact the advertisers who support the show they don't like and threaten a boycott if the companies don't pull their ads. That seems more like blackmail than an actual boycott.
For the record, I maintain boycotts against two local businesses whose owners have been disrespectful to me over the years. I doubt they suffer much without my patronage, and I don't actively encourage other people not to do business with them. I simply take my business elsewhere, so I understand the concept. I just think it's mostly misapplied.