Distilled has one major disadvantage in my eyes, which is that you don't know where it came from. Was it distilled in copper vats, which isn't uncommon for steam distillation? Was it even steam distilled? Maybe it was fractionally distilled? Vacuum distilled? Who knows! And if you buy it from the supermarket machines, each machine is different and you might not be getting the same quality water at each one. With RO/DI it's right there in my basement, I can see what's going in with my TDS meter, what's coming out with my TDS meter, and I have control over it. That's a huge huge deal for me.

So, control issues aside, is distilled good/bad for the reef? Well, that's dependent on one major factor. Did it go through a copper worm after being distilled. Some stills have them, some use stainless. You really will never know without looking at the guts of the still that made that particular jug. That one issue is the only big difference. Otherwise distilled is, typically, more pure than RO/DI, and as Shovelhead pointed out, once you add your salt mix, it's got all the minerals back in it anyway. Personally, I wouldn't even worry about the copper worm because lots of people have run reefs on tap water, and almost all the feed line plumbing in most houses is copper.

Long story short? It's fine to use, just be aware there is a small chance it could go wrong, but it's pretty unlikely.