How would that help? You declare your "salary" wallet, your salary flows from your day job. You run your underworld schemes in another wallet, and ne'r the two do meet.
How do you propose to spend money from your underworld wallet to buy real things - say to buy a car - without revealing your identity to the merchant? And once your identity is out in the open, how do you propose to evade the undisclosed income investigation that will be inevitably follow.
It depends on how much your underground wallet holds. There was that guy who was successful for many years, laundering dollar bills in person.
If you buy a BMW, your identity will be noted and the transaction recorded. If you buy a bagel sandwich, the clerk will forget about you by noon the next day. So if it's small potatoes, you could be fine.
If you have a ton of cash to move, you are right- in person becomes a bad option. That's when you go back to the basics- you launder the money, like every big-time criminal in history.