There are many useful functions on your Mac that can be revealed using the Option key. Here’s a few examples:
By holding OPTION and clicking the volume button in your menu bar, you can easily switch between different speakers:
By holding OPTION and clicking the Wifi button in your menu bar, you can disconnect from a network without turning wifi off:
By holding the OPTION key and clicking on the battery button in your menu bar, you can see the condition of your battery (to see if it needs replacing):
There are many other hidden options that can be accessed using the OPTION key, so experiment and find some that are useful to you!