Let's hear what you think they're used for?That's not what catalytic converters are for at all. And I've tested my same car with and without catalytic converters, I assure you, they have no effect on AFR.
A WBO2 is installed before the converter(s) because the converters alter AFR / reduce harmful emissions. When you install a WBO2 after the cats (which is the wrong way, hence why you never see anyone doing it that way) you're getting a reading that isn't accurate at the engine because the cats (if working correctly) are doing their jobs and reducing harmful emissions / attempting to reach the stoich ratio. When tuning accurately you want to know what the engine is doing AT the engine and not anything behind that where the AFR is changed.If the sole purpose of the converter was to change then afr then why is the wideband 02 installed before it? Converters are there to do just that, convert gasses into less harmful gasses for the environment. Take a little read if you will, How do catalytic converters work? - Explain that Stuff better explanes how this works. As for afr your primary 02 in modern cars (most fuel injected vehicles) the primary 02 sensor(s) are factory wideband afr sensors that are constantly measuring the afr and making adjustments as needed. Do a little more reading. Youd be enlightened by what you may find.
The reason you have an O2 before a cat and after cat is to ensure the converter is working. If the converter didn't do anything why would you even need a 2nd O2...
If anyone needs to read anything you need to read this...
EFI University Electronic Fuel Injection Tuning :: View topic - Do catalytic converters affect AFR?
Will the every day driver notice a difference in a tune done pre / post cat? Probably not especially at idle or normal driving. WOT is a different story. My point was why do all this tuning work on a value that isn't at the engine.