Attempting "difficult" elements in the program BUT not actually completing them does not add value - in fact, it detracts from the program. I learned that the hard way at Mountain Cup in 2003. The following year, I had only elements I could have a chance of successfully completing. It went well. As a skater, it helps to be confident of all elements in the program. It is less stressful and enhances presentation.
However, one still has to remain competitive. I mean, you can't keep doing only single jumps and simple spins your entire life - there would be no improvement that way!
So, there has to be a balance. I have found it useful to have only ONE or TWO elements that are uncertain... and, keep working on them until nothing is uncertain! Keep pushing the boundary, without hurting yourself!