Casinos don't like when low denomination chips leave the table. Let's say you go play craps and buy in for $300. You don't buy chips at the cage you buy them at the table. You have a good evening and have 643 dollars. A lot of $1s, $5s and $25s. But if you look at it you'll see that it's mostly in $25s and some in $5s. The $1s you've been making change for the dealers, win a $24 dollar bit and you'll hear 'drop me a dollar' as they slide you are $25.
The dealers have maybe 400 total $1s on a table that has 3000 chips on it. But they are ALWAYS using them. If one player out of 16 had 100 of them they'd have a problem. If 2 players had them they'd struggle to deal. If and when the table runs out of chips they have to get a delivery restocking them. This takes a long time, disrupts the game and the players HATE it. A number of players will just leave. A large number won't play on a table with a new bank. So the casino tries to keep the change ON the table as much as possible. So when you go to leave what do you do with your 643? you put them in the center of the table and they give you a $500, a $100, a $25, 3x $5s and 3x $1s and point you towards the cage.
Poker is a bit different, but if you buy a rack of $1s, put them in a backpack and walk out you'll get some attention. Even some fun stories about casinos tracking people down not for the chips but for the plastic rack. Some casinos don't care and on a slow night dealers or the cage might help you find a rack of pristine chips for a nice tip. Some won't even sell you a $1 for a souvenir. There are posts on here, just use the search feature and type in 'harvest' and you'll find lots of stories.