Just to put things into some kind of historical perspective, back in the 70's and 80's -- when "runners" made their rounds at sports books all over Las Vegas, the runners usually carried six digits in cash and often much more. The majority of them were, I believe, armed. They often had big fanny pack things wrapped firmly around their waists.
So Alan, when alacrity is important, cash is often the only way to go. These guys were trying to get lines before shifts and did not have five or ten extra minutes to negotiate markers or credit.
Rob's cash-carrying is subtle by comparison. I can see where he's coming from. Let's call a spade a spade. "Recreational player" is almost synonymous (or was in the 80's) with "tourist." Tourists shouldn't carry cash.
If you want to get a sense of what the runners were like, please watch "The Runner," which is a terrible movie, but it does give a reasonable sense of things. Plus it has John Goodman, and I love John Goodman.