I can't believe you guys don't understand how this can be useful. First of all, settings the text size in an editor takes a hell of a lot longer than scrolling the mouse wheel, so +1 for efficiency. Secondly, if someone walks by your desk who can't see very well and you want to discuss the code on your screen, rapidly being able to change the font size is extremely handy. Third, if you connect your computer to a projector, TV, or whatever else, you can easily adjust the font size without making everyone wait.
Regardless of the incredibly obvious things I already pointed out that no one should ever have to explain, there's also the benefit of adapting the font size for your own benefit when environmental changes are outside of your control without wasting time. If you're at a park outside while working on a laptop, it's basically impossible to read tiny fonts sometimes. If you have addons that modify the code with squiggly lines, it can be difficult to see colors when the lines are small. If you want to get a general sense of how your code looks, you can do your own squint test by zooming very far out so a lot of your code is on the screen at once. On that note, if you want to see more code for a short period of time even though it would be uncomfortable to write code with a smaller font for a long period of time, you can easily do that.
In short, you clearly have a malfunctioning brain if you don't understand how this could be a feature. It's totally fine if you want to turn it off, but acting like the person who came up with it is the stupidest person to have ever walked to earth is idiocy, plain and simple.