This. When I was in college, I briefly delivered pizzas, and ended up with lots of $1 dollar bills from my tips. There stack was too big to fit in my wallet, so I slapped a rubber band around it. The rubber band wadded up the singles into a roll.
I didn’t mind, since it looked cool ($100 in ones is so much better than 4 $20’s for a poor college kid’s ego). Which is probably another reason why it’s used in movies.
That’s because Tuco was getting his rolls delivered from his lower level guys who do keep it in their pocket, at least that’s my assumption. Notice that WW had flat stacks once he processed (counted) all his money.
When I was playing poker, I had to deal with a lot of cash. The easiest way to keep track of it and store it is to roll it up into $500 or $1000 rolls and put an elastic around it. The money stays protected, the rolls don’t come apart, and you can just throw them in a coffee can or whatever. Very handy.
Flat stacks of bills are usually banded with paper bands. That’s maybe how money comes from the mint, but if you try to maintain your own stacks like that you wind up using rubber bands, and then the money curls. And when it does, the bills on the inside can easily slip out.
The traditional way of carrying a lot of cash is with a money clip - you fold the bills in half and then clip them together. That works fine for smaller amounts.
Rolls with rubber bands are easy to store, easy to count, and they stay together.
Actually a friend is a math major. He’s spent so much time doing quadratic equations, he can’t subtract one two-digit number from another. (I have no better excuse than old age.)