Over time which of the two is outside the other varies from stock to stock or at differing points in a stock or ETF movement. One thing that seems universal is that an excess in price above or below both bands is time to look for entry or exit points. Or at the least consolidation. The faster the time frame the faster one must act. It is a vital part of my 5minute intraday signal chart for scalping. I use them in all time frames. As in any TA one looks for confirmations from indicators, ma's and ema's, money and volume to not enter too early or hold too long.