Fun part is when you go back to your old code you thought was hot shit when you wrote it, and you were so, so proud of it, and realize you could of written the entire thing to run 4 times as fast in half as many lines. 
Done this a lot. Although it’s usually more like it executes faster than I can blink instead of 5 minutes, and in a tenth as many lines.
Eventually you even start writing code you can actually understand when you come back to it after a while!