Probability will be a moving target as well, because time and movement of the underlying security will adjust the percentages as you go. Nevertheless, the power of delta can be used in several ways to design your options strategies. Of course, delta is just one piece of the puzzle when looking at trading options. For the experienced options trader, accessing an approximation of the probability of profit can be a powerful tool.
Another way that traders use delta is to measure their exposure to the underlying stock. For example, if a long call is showing a delta of .30, the trader might think of the position as if he were long 30 shares. This may simplify the analysis.