The major reason for all this coin mixing thingy is to avoid scrutiny and abuse of privacy from Government and not a common person like me who doesn't care about where you got your coins from, where you send your coin to, why you send your coins from A to B, and what you spent your coins on... Think about it
Not Really
I don't really enjoy the fact that anybody that knows my address can know the amount I'm having
Where it goes and where whence it's coming from
It's not limited to hiding from the government.
The person is confused and you are correct. This creates a huge security risk both for online and physical payments, it is significantly worse in physical payments. There is a face attached to the payment, and if they look up your change or related addresses then they will know your Bitcoin wealth. Obviously this presents a great opportunity for an attacker, and they'd have definite proof that you do have this amount -- so any kind of trickery with different passphrases, dummy wallets and whatever other in person excuses will not work against such a criminal. One-time payments would be very risky, regular payments at the same establishments would be a guaranteed ticket to a bad outcome eventually. The alternative is simply using wallets as single-purpose and dumping them afterwards, but that comes with extra work and is error-prone too.
Are you saying you reuse the same Bitcoin address for everything?
No, that is not what he is saying.
You can largely improve your privacy by using coin control, different addresses and even different wallets for different purposes.
Which requires a lot of knowledge, skill, and is very error-prone. A single mistake can undo a lot of the work that has been done. Mixers are better for this, and the user and philipma1957 are right about this. The primary good use cases is shielding from the recipients without the use of custodial platforms for wallet purposes. Mixers need a come back, users should have easy access to reputable mixers.
