IMHO pivot is an obsolete indicator. It was originally designed for floor traders before they had computers with moving averages.
Pivot basically mimics a 20 period exponential moving average on a 15 minute chart. With the 15-minute ema - when it is sloping, you look to buy or sell in the direction of the ma. When it is flat, like this morning on the S&P, you ignore it.
The short coming of pivot is that it doesn't tell you when to ignore it and it doesn't adapt to afternoon price movement as does a moving average.
S1, S2, R1, R2 are basically levels of a Bollinger Band or envelop around the moving average.
Do a visual backtest of pivot versus the ema and you will see what I am talking about.
Bottom line - why use a static indicator? I suspect, even floor traders have moved on to using moving averages.