A large variety of goods and services are available as businesses try to differentiate themselves in the market. Economic activity is encouraged because you need money to live and need to engage in economic activity (through employment or self-employment) to make money. Freedom of individual choice is possible to the extent that the market provides options for work, developing a business, and purchasing goods and services (so long as you can afford them). 
But on the other hand!
Disparity in wealth and mobility exists in market economies because wealth tends to generate wealth. In other words, it's easier for wealthy individuals to become wealthier than it is for the poor to become wealthy. Environmental damage results with no government regulations because it's usually more expensive to produce in an environmentally-sound manner, which reduces profits. There tends to be a reduced social safety net, including such programs as unemployment insurance, Social Security, and Medicare, because these programs are supported through taxation. Poor working conditions can result due to a lack of government regulations because health and safety cost money, thus reducing profits. 
A Market economy is an Economy where supply and demand determine prices and ouput. In practise most are Regulated markets where governments intervene to prevent or limit Capitalist abuses like Monopolies. Laissez-faire economics allows Rich people to take advantage of the rest.