I can use a pad that is slightly tattered on a hard paint system with great results where the same pad on very soft paint will sometimes leave behind some marring and cause more work for me so as my pads get a little worn I use then on harder paint only and open a new one for softer paint systems.
There comes a point where a light cutting pad gets kind of soft and begins to behave more like a polishing pad and I may just use it for that purpose. When I start every job i do a test section to determine which pad, product, machine, speed setting, arm speed etc works best on that particular vehicle and I may not like how an older pad is working out and switch it out for a new one.
I sometimes (as I believe we all do) get some real nasty vehicles where the owner doesn't want to spend much money but just wants a significant improvement. This is where these old worn out pads come in handy so I don't throw pads out when they are showing signs of wear. If I did then I would have to ruin a brand new pad on a dump truck that I am challenged with making look good on a customer's tight budget.
Then there are the buses that I do from time to time. I will use some awful looking pads that most would have already thrown out long before on these buses. I typically buff out the gel coat with a wool pad then use a cleaner wax with a ratty old but clean foam pad.
It's kind of like when a $5 microfiber towel begins to leave marring on black paint, it then gets used for light colored cars, then to door jams, then to scrubbing or drying carpets, then to engine and under hood tasks.
Clay gets a little old then it gets used on wheel faces and when it gets too dirty for that I use it on the barrels of wheels before throwing it in the trash.
I'm in this to make money and not to spend money so I find a use for everything that I own until it no longer serves a purpose then it gets trashed.