The depth of the fret slots on a guitar can be a personal preference. Some people like them super shallow, while others like them a little deeper.
Ultimately, it’s up to the player to decide how much depth they want.
However, there is one general rule that should always be followed when fretting: make sure your fingers are able to slide easily in and out of the slots. If the slots are too deep, your fingers may get stuck, and you’ll have to pull them out forcefully in order to play.
This can be really frustrating and cause you to lose concentration.
If you’re unsure about how deep your slots should be, start by checking out some guitars that have good slots and then experiment a little bit until you find the perfect depth for you.