When I was taught to count, our instructor recommended tipping to encourage pen and service, as you would tip a waiter in a restaurant.
Lately, I think most dealers are too dense to realize you are seeking improved pen. So, I tip lightly to encourage friendliness and to appear to be a ploppy. So, maybe, just maybe, it provides a little bit of camouflage.
Also, if you are a high roller I think it is expected. If you don't tip you might attract attention as a cheap skate