I think it depends how it's set up... and to either avoid (in non-tipping situations such as simple checking out of a store ... or adjust to a different amount/percentage).
I've seen one at restaurants set up to give you the options of tipping 20%, 25% or 30%... and while I was planning on giving 15%, even though I felt like the waitress basically ignored us (some simple water refills would of been nice)
The fact that it was setup for a minimum of 20% upset me a bit... especially with waitress basically ignored us. Had to figure out how to get it to a lower amount.
I will say, for restaurants, I like when you can set it up as a percentage... instead of having to do the math for a dollar amount.
