And I think the purpose of having an assembly is criticizing the government.
In this picture , you can see there is a group of people.( However, it's just 3 people, don't care about it.) On their white boards, they said:" Low Tax, Anti- Gov and I want a Job!" And thier faces expressed they are angry to the govenmen and dissatisfied with their policy.
There are so much reason for having the assembly.This picture also shows us citizens can have an assembly whenever, wherever they want. ( I don't sure about it, because in China, citizens can't have a assembly without announcing the local government, if you don't do tha, the police will arrest you, they say you broke the social order.)
And why the freedom of Assembly is very important because the government can know which part they didn't do well and how they can improve. And too many assembly happened continuously, it may mean citizens need a new government and a new system to instead of the old one. That's terrible. Also the freedom of Assembly shows people wanting and it also is a way to fight for their rights.