The Items per Row variable allows you to create pre-defined sets which can be used throughout Items per Row options in your admin. See Items per Row Option.
Set up as many variables as you want for different items per row column splits and assign them in each module (Banners, Blocks, Products, Gallery, etc.) and everywhere else there are column based elements like the general product listing on category pages in Journal > Skins > Edit > Product Listing > General > Products per Row.
You will find a selector for Items per Row throughout the Journal admin (skin, modules) where you can pick a variable or Custom, in which case you can define specific rules just for that element or module without using a variable.