The Following is why.....

.....Park Rangers and employees strongly suggest you follow recommendations from them and the signs you see along the trails.
DEATH IN THE SMOKIES
On Sunday, May 28, Great Smoky Mountains National Park Rangers received a report that a 37 year-old male fell from the top of the 100-foot tall Ramsey Cascades waterfall late that afternoon. The man, who was hiking alone, was observed climbing across the top of the waterfall before he fell. Park Rangers immediately responded to the scene and determined the individual, who had fallen approximately 80 feet, was deceased. Rangers recovered the body on Monday, May 29.
....And not to minimize this mans loss in any way, however this could have not happened. It is Sooo! Important for visitors to the GSMNP, and any other protected area to listen to and follow suggestions form Rangers.

I have volunteered for like 9+ years in the GSMNP and listened to park service employees, and other long-term volunteers tell of similar horrible mistakes made by folks who thought they were exempt from the dangers noted on a sign or what had been explained to them by a Ranger. 
This feeling of "oh, it'll be alright, I've hiked in the glaciers of Alaska", or, "oh, I'll be fine I've done this before", does not mean you won't slip this time. 
Peace and awareness to you all as you hike the path.