For a lot of things like a toothbrush they normally have these recommended amount of days where you should replace the product despite if you think you can get more out of it. I know most people usually never follow those either as a way to save money as they usually question whether or not that date is simply a way to get you to keep buying more faster.
I think for myself the only type of items that I pretty much do follow when it comes to expiry dates are for say certain food and beverage products that have a best before date. Then again, I guess that can be a little different as those are not a how many uses type of deal.
For wear and tear on a product I personally usually do just go based on what I see/feel as oppose to what the box says personally.