I think he meant the piece of mind of just using the data without hitting any overage or an actual limit, regardless if it was throttled. I have the unlimited data plan.
I know a lot of people who have to take a look at their usage meters and if their limit is approaching, starts to use their smartphones less on cellular and wait for a wifi connection. I don't want to be like that, just have to enjoy the phone for whatever I want to use it for, and the grandfathered unlimited data plan helps me do that.
Now I know the other features the mobile share plan have, that's a good thing for them to advertise, but I'm afraid if I use one of those tiered plans, I do gain those but I risk what I said earlier and more importantly I lose the ability to subsidize my phone (for now since AT&T still offers it) which is one I really like and I plan on staying with them.
Now of course this is really a case to case basis, to me unlimited works perfectly for a single line. Oh and btw, 30GB
isn't unlimited