Ok, maybe I'm thinking too hard about this, but...
Some players might be giving away the strength of their hand based on what kind of chips they're using to bet.
Bart talks about how he likes to use big chips to spike the pot when he's value betting so he can make the pot look bigger and value bet larger amounts on future streets.
So by that logic, you can use big chips when you're value betting on the flop and turn and then a whole bunch of non-threatening red chips on the river to make your river bet look smaller and the pot look bigger.
And then when you're bluffing, you can use a whole bunch of red chips on the flop and turn and then black chips on the river to make the river look like a big scary bet relative to the size of the pot.
But if you don't always use the same types of chips for certain bet sizes, doesn't the kind of chip you're using become a kind of tell?
I've mentioned before that I insist on being balanced, even when unnecessary. So my standard is, if I have to use more than 14 chips, then I'll use the next denomination instead. If I'm betting $70, then I'll use 14 green chips. For $75, 3 greens. For $80, three greens and one red. For $350 I use 14 greens, but for any more than that I start using black.