Days are declared for remembering someone are according to the government. Not only government decides the days but also public will decide the days followed by government.
Mostly days are meant to celebrate some one greatness of something greatness. In many countries independence day is celebrated very well.
In countries like India not only independence day. There will festival in every day of the year in different places.
The government had officially declared only some days. that might be around average of 10 days in a month. These days were also working days.
So knowing about this days will improve general knowledge power in the society.