Waste of money, and takes up filter space that would be better used with more bio media or mech filtration. There really is no need to run carbon on a tank full time. There are plenty of threads in carbon's uses and misuses.
I've used carbon in every planted tank I've ever had, and didn't have any problems with the plants getting their nutrients. IMO it's up to the person if they want to use carbon or not.
Here's a couple pictures of my tanks from the past.