If you’ve been running WordPress for a long time, or if you have a complex site, you probably have lots of categories. However, lots of categories causes a usability annoyance when the categories box in the admin screen stays pretty small.
The solution? Make it bigger!
The following code can be added to the functions file of your theme and it will make the categories box taller.
You can change 500px to be anything you want. Make it bigger or smaller.
Of course, you could always clean up the categories so you have less. I should do that, but I’ll just make it taller for now. 😉