A vision statement is where a business outlines where they want to be in the future and it communicates both the purpose and values of your business. 
A mission statement shows how a business will get to where they want to be in the future. 
Personally, I don't think that vision and mission statements are necessary for every business. For example, when people are buying from my cupcake business, their concern is not what the vision and mission statements say but it is about how good the cupcakes taste and are they a value for the consumers money. However, these two factors are important when an employee is looking to work at a company. They need to see what the company stands for and what they want before the employee can decide to take a job there. 
Secondly, vision and mission statements are necessary for large corporations of any size and especially businesses in the service sector. Their statements show their values and how they treat consumers. In my opinion, these are most important in the health industry, schools, hotels and aircraft companies.