Well really I think it's done out of pure common sense. You would feel funny driving your expensive new car 60mph down a dirt road. You would feel better driving your old beater around on the road. That is where the concept comes from. I just suggested this to MT just because I think he may jump down the rabbit hole in needle purchases. From what I read he buys a lot of new records so maybe he will be fine with one table. I only own one tone arm but I don't play much old ruff vinyl. The new stuff sounds so good.
It's just that you don't want to play a beat-up record on a $5K cart, it just doesn't feel right. It's better to play it on a cheaper cart. Much of this feeling comes from hearing really big pops, that's all. Some cringe.
The other concept is say you have 3000 records you purchased at a garage sale. You don't know what 3/4 of them are. Are you going to spend 20 minutes a record and wear out your cleaning machine cleaning every record? Are you going to put every record on your main turntable and possibly ruin your best cartridge in the process? For this person another turntable is necessary. If you buy only new records one arm would be fine.
If you think about it, there is a valid concept of a rough record helping wear out an expensive needle. This is where it comes from.
Actually there are more high-end turntables sold now than ever. Turntables are actually better now than they have ever been. The science of LP reproduction has continued to evolve, where tape has been left behind. Just a run though Needle Dr. will show you how big owning a turntable is. Good luck.
If one is in a position financially to have a dedicated turntable specifically for rough vinyl, I can see how that could help. I just don't think most people are so fortunate.
Personally, I try to avoid vinyl in poor shape, not because I fear for my stylus, it just sounds bad!