Bananas are rich in potassium, which is good for your heart, muscles and nerves. Especially for athletes since they lose a lot of electrolytes. They also come in handy with digestive problems like diarrhea, where a lot of water and electrolytes are lost.
To reduce bloodpressure, it is widely known that a reduced sodium intake is crucial, but potassium is just as important because of its vasodilation effects. They reduce the chance of developing asthma and cancer.
Bananas are available all year long around the globe. Most of them come from Inda when they are still green. You should get them light green to have more time before they go bad and store them hanging (just like they were born) to avoid black spots. But don't put them in the fridge, they will start to discolour.
My tip is to make a smoothie out of them: two apples, one banana and some orange juice. That results in around 600-700 ml and is a great way to start a day or after a workout since it is easy and fast to make.