Actual Plays can introduce you to new styles of playing and DMing and improve your skills at the table. For example many people started running planescape campaigns due to Rolling With Difficulty. Before RWD, lots of people had no idea that D&D has spaceships and what is essentially a sci-fi setting. If you're a GM who wants to get better at running the game, then obviously my first recommendation is Matt Colville's videos, but try listening to a few different actual plays and learning from the styles of different GMs. Maybe you hate the way Matt Mercer runs the game, but you really like how Brennan Lee Mulligan does it. Maybe you didn't know it was possible to run the game in a different way than how Matt Mercer does it. If you don't have three decades of experience playing with diverse tables, then actual plays provide a substitute for that experience.