If this is your only value, text is fine - however - if you have an administrative back end, you are very likely to have at least a few and should have a LOT of configurable variables.
- per_page (the one of which you speak)
- Page titles - what if the owner wants to change their shopping cart heading from "Shopping Cart" to "Shop for Widgets?" And . . . they don't know how to, or you don't want them futzing around with, the HTML/PHP?
- Owner email, for responses, email functions . . .
- company name, number, address for display in various places . . .
- CSS selector names used by your scripts, so these can be changed if the owner experiments with different styles
You get the picture. One of the biggest problems I have with most existing code I'm asked to "fix" - nearly all of it has hard-coded values in places that should be variables that are either set at the head of a global include or extracted from a database.
If you extract them from a database, they become configurable, if they are configurable, your project is portable . . . . and you can see where that goes.