Decentralized grid will have less ability to deal with spikes in load, and be more unstable as a result. Question in cases like this is often - do you want to have a lot of smaller outages all the time or bigger, but less common outages.

The answer to the genre of questions is that you always want fewer small problems, and more day-to-day efficiency...

... until the big disaster actually happens at which time at which point it's simply criminal that such things were allowed to happen.