This website is absolutely amazing to use. If you're not sure how the monsters you plan to run will operate in battle, this guide helps better coordinate the battle. Sometimes the DM might have the monsters pull tactics and maneuvers that the creature itself wouldn't think to do or even conceive of doing like a troll using skirmishing tactics or certain monsters using ambush tactics. There's a guide for almost every monster so that whatever you plan to run, you can pull the website up and see what the monster would realistically do in a combat scenario. I plan to use this myself so as to not punish my players too badly and be as accurate as I can be in this world I've built.