There is no benefit to rollover data. Verizon uses plan data before roll over and this is the problem. In order to get roll over data you must not use all plan data for a month. If you accomplish this, the following month you have plan data plus the remainder from last month. Now in order to benefit from rollover data you must first use all your plan data for the month which inevitably ensures that next month you have No rollover. This is why its useless. Verizon needs to use rollover before plan data!
It came in handy when I was travelling one month and used more data than usual. That didn't seem useless to me. Verizon can certainly set up carryover the way it wants as long as they disclose how ti work, which they do. It work exactly like AT&T rollover.
While I do agree that there would be MORE benefit to me and other customers if the carryover was used first, I have to disagree that there is no benefit with it set up as it is.
If you have a plan that is in line with your usage, most months you will have some data left that will carryover. On those occasional times you need just a bit more, it's there. Most months (all, actually, since I've had carryover) I don't use all my plan data and have some to carryover. I'm sure the month will come when I'll be glad I have that cushion.