A lion's mane (only found on male lions) is used to make the lion look bigger and stronger to scare away other animals.
![lion's mane](https://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Lion_waiting_in_Namibia.jpg/320px-Lion_waiting_in_Namibia.jpg)
(From: Wikipedia - Lion)
You can tell how healthy a lion is by looking at it's mane. The thicker, fuller and darker the mane is, the healthier the lion.