The catch? Your GPU has to work twice as hard. If your card is gasping at 1080p, it will have a heart attack at 4K. If you have ever watched a hardcore iRacing or Assetto Corsa streamer, you might have noticed their screens look... square. They aren't using old monitors; they are using custom resolutions to crop the image.
Always check "GPU scaling" before creating a custom res. If your monitor fights the new resolution, let the graphics card handle the heavy lifting. Your monitor won't know the difference, but your frame rate will. custom resolution
But when it works? When you force a demanding game to run at a perfect 1728x1080 (a popular "stretched" resolution for competitive shooters) and your aim suddenly feels snappier? You realize that the default settings are just a suggestion. The real power is in typing in your own numbers. The catch