Getting the most life out of your climbing gear is not only a smart financial decision, but it's also good for the environment. The materials our stuff is made of (various metals and petroleum products) have a high environmental cost. That being said, pushing our equipment beyond what it was designed for is kinda dumb.
It's not the end of the world for clothing or camping gear, but taking the equipment we use to protect us in the event of a fall out of it's intended application (or beyond it's intended lifespan) can have serious consequences. When climbers (myself included) look at a worn out piece of gear and say, "oh, it's fine" that's a great example of poor decision making. That decision is usually not based on any actual scientific data. Instead it's most often based on some combination of laziness, a short sighted need for that piece of equipment, and frugality.
What brings all this to mind is a study I recently came across from The German Alpine Club. Every time we go climbing (unless it's bouldering) we're using slings (runners, quickdraws, etc) of some kind. They don't last forever. This study took a look at the strength of sling material as it ages, and if there is any correlation between a haggard appearance and a loss of strength. Pretty interesting reading.
I am not a scientist and have no science background. I'm pretty sure that for something to become accepted science it takes more than one study. That being said, the above paper presents information that is waaaay more fact based than guessing and hoping for the best. If you're interested in a bit more reading on sling material selection and use (or just have some time to kill at work) check out this article from Rock And Ice magazine and this video and article from DMM. Both look at appropriate applications for plain nylon and dyneema slings and quickdraws. There are more links at the bottom of the DMM article if you really want to fall down the rabbit hole.