This is not really necessary. But it can be useful if you want a bit more flexibility.
In this step you can add a specialized environment variable pointing to your personal libs. However in kicad 4 there is no direct way to use this variable. (The only place i know of is in the template projects.)
This does not add it to the search path of eeschema. (That must be done in the component library dialog of eeschema/library editor)
In current nightly (will become kicad 5) you can use environment variables in the same manner as you can now with footprint libraries.
From the wording here i assume you are running kicad 4.0.x.
Adding the search path is only half the job. You also need to add the library it self.
One possible problem comes to mind if you did both and still can not see your symbol. In kicad 4 a symbol name must be unique over all libs. Otherwise kicad will use the one from the library with the highest priority.
The same holds true for library names. It must be unique otherwise kicad takes the one from the search path with highest priority.
More details see here
Another thing to remember is that the component library dialog of eeschema controls only the current project. Meaning if you want to access your lib in a different project you will need to add it to that as well. (Only option for global addition is by manually editing the kicad.pro template project.)
By the way the component library dialog also exists in the library editor.