I think the point is to take them up on the offer, but hopefully not need to use it.
I think the deal is that you copy your site to their servers, then you have a choice of what to do.
Change DNS before the storm "just in case",
or
Change DNS if your other server goes down, so that you won't be without your sites for an extended period of time.
It sounds like a win/win situation to me, and I think it is really great that a company would offer something like this for FREE with no obligation.
