Protein shakes are an excellent idea for anybody.
Depending on your goals depends on how much you take. I have about 3 a day. Although i am looking to put on weight, i can actually lose fat while still having 3 a day.

You should always take one after a workout, to replenish what your muscles have lost during the workout.
They stimulate muscle growth, help with muscle recovery and generally replenish the body.
What are your eating habits like? What are your aims?

Protien is just something that is in everybodys diet. It isnt some mad chemical to be aware of. A higher protein intake can consequently lead to fat loss due to higher muscle mass, can obviously lead to muscle growth. It can stimulate metabolism boost, again leading to fat loss and aids muscle recovery.
Shakes are just a quick and easy way to get a high dose into your blood quickly.