Back when I first started developing client/server apps which needed to make use of HTTP to send data to the server, I was pretty nieve when it came to HTTP methods. I literally used GET requests for EVERYTHING. 

I later learned that I should use POST for sending data and GET for requesting data however, I was slightly confused as to why this is best practice. From a functionality perspective, I was able to use either GET or POST to achieve the exact same thing. 

Why is it important to use specific HTTP methods rather than using the same method for everything?

I understand that POST is more secure than GET (GET makes the data visible in the HTTP URL) however, couldn't we just use POST for everything then?