Probably the chief advantage is that the plug electrode doesn't stick out as far, allowing the piston to come up that much further, and the engine to have a bit higher compression or the combustion area to be a little bit tighter. This is the only true advantage of these, and it's probably why you'll find them as OE on some German stuff.

They're also much harder to foul. Ish. If one of those gaps gets fouled with oil/carbon, the whole plug's basically shorted, so I don't know about that.

Beyond my very first comment about plug reach lies the world of marketing speak, where these plugs might be said to "increase flame kernel area" and all sorts of other crap that sounds good to a layman's ear, but sounds like marketing BS to anybody who understands the sparkplug, the cumbustion chamber, and how all of that does its job. You can't really claim it even makes the plug last longer, since as you see from the pic, there's a single electrode in the middle that wears out fast enough, just like a traditional plug.

There may be just a few ticks of improvement in emissions due to the plug's configuration making a few less unburned hydrocarbons. But soooooooo much of that has everything to do with combustion chamber and everything else.

When it comes to plug design, those in the know realize that installing high tech looking plugs like these is kinda like using a really expensive lighter to light a candle. It may do the job very well, but no better than any old BIC, meanwhile, the candle is the most important bit if you care about candle performance.

So, TLDR- They're pretty much a gimmick, though they do allow for a bit more performance if the engine is built specifically to take advantage of them from the start. Otherwise, consider how many other thoroughly modern, obsessively engineered, cutting edge engines still use a traditional looking plug. There's a reason why.