What "ability's" could be gained from using 100% of your brain?

We do use 100% of our brains. Only some of it is used for conscious thought. But the rest of it is busy taking care of all our other functions.

We actually don't use 100% of our brain. Only about 12% of our brain is functional.

That is a myth.

http://www.snopes.com/science/stats/10percent.asp

Not every section of your brain is significantly active 100% of the time, but all of it is necessary and is used.

The brain is an incredibly expensive organ. 25% of all the glucose we consume goes straight to our brain. We would not have evolved so much of such an expensive tissue only to let the majority of it sit and do nothing.

We may use the entire brain, but only bit's and pieces from each part.
It's not like we use only 12% of our brain, so the lower left hand section.