Nope, I don't know who you're quoting here but it's nonsense. Earlier in the thread someone posted about changirear pads without changing the discs. This was and is common prractice and is perfectly safe as long as the discs are within manufacturers' specs as engraved on the discs.Sorry but you're being a bit disingenuous here.
"While it's possible to replace brake discs without changing the brake pads, it's not recommended. Brake pads and discs wear together, and replacing one without the other can lead to uneven braking, reduced performance, and potential damage to the new components. It's generally best to replace both brake pads and discs simultaneously to ensure optimal braking performance and safety."
The only reason new pads will need time to "bed in" or "grip the old discs" as you put it above is if the wear on the old discs is uneven and they are grovved and/or pitted. Two perfectly flat surfaces properly installed need no time to "bed in" to deliver excellent braking.I think a lot of places now recommend replacing discs with the pads, experienced same when having my Mazda serviced by the stealership.
Some of it is just money grabbing but also safety. If there is a lip on the discs through wear when you replace the pads it will take longer for them to settle in which means less braking force.
Which I have experienced in person when changing pads on my cars in years gone by. Could take a few days for the new pads to grip the old discs but the discs were pretty worn in fairness.
I didn't mention anything about grooves or any type of damage to the disc/rotors. I do however have experience with replacing brake pads on used discs/rotors and if you don't know what you are dealing with you will rear end another car super easy!