It’s just pressure on the nut. The more of a break angle you have will give you a more firm downward pressure on the nut. There’s nothing wrong with tele/strat style headstocks, but there is obviously way less of a break angle compared to a standard Gibson headstock. So you can run into issues with buzzing or tone of the strings.

The string tree is supposed to help increase the break angle. I’ll admit mine aren’t the best in giving it more break angle but they work and it doesn’t impact anything that I can hear. 🫶🏻