I'm adding some heavy lifting to my functions file but I'm wondering if there's a better way to do this. I'm going to add some functions relating to shipping in my ecommerce site. It will be looking up the buyer's shipping state or zip and hiding a shipping option if set as excluded.
Since I only need this function on the checkout page(s) if the code is in the functions file, is it running every time any page is loaded?
Is a plugin a better solution or do they both actively run from every page load?