Waterfalls

Personally, I wouldn't use a waterfall.
1. As far as a I know, waterfalls aren't found in their natural habitat. I don't like adding a lot of things that aren't in their natural habitat (such as sand, waterfalls etc).
2. I would be afraid that the waterfall would add too much humidity to the tank. Too much humidity over long periods of time can (I believe) cause respiratory infections.

I wouldn't trust yahoo answers. A lot of the people on their just answer questions to gain points. I've found a lot of the answers people post are copy and pasted from the first or second link that pops up if the question is googled. So I never trust yahoo answers

It would be a benefit in the winter when the humidity goes to low. It will help with shed and hydration as moving water draws attention to the leo, however in the summer it cannot be used due to the elevated humidity.

A proper humid hide would take care of that, though, Herp.

Depending where you live the enclosures can drop to like 10% in the winter and some of these little rascals don't make use of the humid hides. I am sure you have seen many people in panic asking for help due to stuck shed

And a simple warm bath can cure that.

Some geckos have serious water phobia and act like your trying to drown them. I rather prevent the problem keeping the humidity up at 40-45 than stress a gecko out.

i only use waterfalls in a humid based tank, my old Aviculria Aviculria (tarantula), My old Iguana, and my old Veiled Chameleon all had waterfalls, and the difference i saw from adding it was high, before the humidity was around 20%-40% lower (depending on the size of the fall) without it then it was with it.

If you desired the look of a waterfall in your viv, I would suggest a minimum tank size of at least a40 gallon breeder as getting a good waterfall to fit in anything smaller likely won't happen.plus putting it on the cool side with a screen to will help alleviate the too much humidity problem. I personally wouldn't use one as it isn't natural to their environment, but some people like the look of it.waterfalls are difficult to maintain and operate properly, but if your looking to add humidity to your tank and your leo isn't fond of their moist hide (which I haven't seen a leo refuse a most hide when you use, moist paper towels instead of moss, my leo won't use a moss hide but loves his paper towels) you can use a shallow dish like a soap fish on the hot side of your viv to add moisture to the tank.