On the surface it does not seem that advantageous. I remember having the same thoughts when I first had access to it, you know, when it was a talent and all:).
However, as time progressed and I began playing with another person, druid, the benefits became more evident. The primary one is that I hit that oh s%@t button and they can heal you through it. Works great in instances, works great in BGs and works great in PVE.
THen in BGs, after you gain the attention of the opposing faction by obliterating a few of their team members, you can block while they sit there and use cooldowns on you, and while they hit on you for those ten seconds or so. And I have to laugh at them, seems they just dont know they cant do anything to me. This gives time for a team member to pull that person off of me, or even to heal me. Either way, I usually have blink or a Frost nova, blink macro to where when the Ice Bloc runs out, BAM, I freeze them and blink away. With all the confusion, they usually have minimal time to react, much less know where I went, which gives me time to get the hell out of there, or help finish them off if they are low and team members got to that player in time.
Ice block, drops aggro. Ice block clears DOTs. You find yourself in an instance where your huuuuge crit suddenly pulled threat off the tank, BAM IB and threat is dumped.
Most importantly, it allows YOU to assess the situation and think of someway to either recover and finish your task at hand, or to be able to get the hell out of there and come back to finish the job.
SO, you see, it has many uses in both PVE and PVP. Also good, if you are almost OOM and playing with another or a group, the mob is on you, and it will allow your party to finish it off.