Boycotts influence policy.  It also makes me feel better.  You buy whatever you want, I'll do the same.  Every time I buy an I boycott a French product, it hurts that company.  My little bit helps.  The last time I checked, French import sales were down 10-15%.   French tourism sales were down 20-25% from America.  That hurts.
When I buy an American product INSTEAD of a French one, it helps that company, more American workers, and keeps my money here.