Any reason to add CYA with more salt?

My pool equipment manufacturer says that I should add 1.5 lbs of CYA every time I add a bag of salt to my pool. I'm wondering why they would suggest this. Is it because by the time that I need to add a bag of salt, the CYA is probably a little low? Or is there some other reason why they'd suggest that?

Ironically or not, in the interval between the time I need to add another 40lbs bag of salt into my pool, the CYA is down about 20 ppm or so. I try to keep CYA close to 80, so my FC level can stay around 4.0.

Thoughts?

Salt and CYA both mostly stay in the pool water although I suppose some of the salt is consumed. They are both mostly lost to splashout and backwash.
So... if the ratio of CYA to salt is 1.5/40 and your target CYA is 80ppm I'd surmise that the target salt is 2133ppm. That doesn't sound right. Maybe they're factoring the consumption of salt in this rule of thumb.
I'd still stick with dosing CYA based on test results and not blindly follow the rule of thumb. However, adding salt is probably a good reminder that you should check the CYA level.

And that's actually what I've been doing, BigDave. For my salt system, the manufacturer's ideal range is between 3.0 and 3.5 (it functions between 2.0 and 4.0). When I see the salt reading on the unit is 3.0, I dump a 40lb bag of salt in the pool, and it bumps it up to about 3.4 (the readings can vary, but that's about right). At that time, I do generally check CYA and it may be under 50, so I'll add CYA to bump it up, hopefully, to around 80. I haven't ever done the math to figure out how much CYA I'd need to add to make a +10 movement in the CYA reading, but since I just added a 40lb bag of salt, I'll try to add 1.5lbs of CYA, roughly (I don't measure, just go my product level in the 5lbs container it comes in).