Yeah as above I was also about to say. The grooves were originally used down so the timber could breathe and didn't rot between the connections. Somewhere along the line some suit decided it was good for grip and is now policy to have it up. From my experience it can be fucken dangerous when wet with less surface area for your shoe to grip, especially when in a shaded spot. Hardwood is even worse and on some jobs we've had to put put sand down to make it safe (while we're there anyway). We used antislip tape along the front edge of any steps when we built our deck, mainly for oldies.