That's simply because it reduces the «no brainer» aspect of the unlimited plan, and forces potential subscribers to do a little math based on their habits. (fortune.com)
A common recommendation is just not to worry about it until your portfolio is quite large, but I'll do a little math for you below. (kevinoninvesting.com)
So if you want to give your pet a human food treat, you may have to do a little math first. (everydayhealth.com)