What functionality is missing? What is unsatisfying with the current situation?

Problem

In the current layout, it is extremely easy to accidentally drag a category to be nested under another or reordered without meaning to. (Especially if you have any sort of shake in your hands--I would say this is an accessibility feature.) I've often noticed my categories are out of order or one is "missing" (hidden under another) because I accidentally dragged it.  

Solution

Add a simple lock/unlock toggle that allows a user to choose to enter a state where they can reorganize categories and nest things, then leave that state when done.  

How does this feature request address the current situation?

It's easy to reorganize things if you want but it isn't done accidentally when a click becomes a click-drag.  

What are other uses for this feature request?

I'm sure there are probably other areas where a lock/unlock could be useful.