For me, it is the perfect balance of suggestive clothing. The ultimate tease of knowing that if there was just a tiny bit less material, you would be able to see it all. This works better with women than it does for men, but I've seen some damn good seductive outfits in the men's camp now and then.
The opposite is almost as true...fetish outfits that show the naughty bits, accentuating them a bit, whilst covering the parts we see all the time, can be quite a turn-on as well.