Technical traders use all sorts of timeframes based on their goals to find potential support or resistance. Day traders tend to focus in on minute time periods, while swing traders and long term investors use the daily and weekly charts.
For years now the stock market has trended higher and higher. As far as finding resistance, most stocks are at all-time highs, so there hasn't been much need to look at a chart that is higher than the daily chart. The S&P 500 (NYSE: SPY), for example, is at all-time highs, so any resistance is just the prior high, which was just a few days ago. Why look at a weekly chart that will show the same thing?
Not every stock is at all-time highs, though. The retail space has been hovering at lows for quite a while now, and many names are starting to bounce off those lows. While it's early to say if they have bottomed and will trend higher, there is still the possibility that you will be enticed by the recent bounce.
If you were to look at a daily chart of Gap, Inc. (NYSE: GAP), for instance, you would see that it has spent the last few months pushing aggressively higher. Just looking at the daily chart would likely cause you to consider a trade here, but don't forget the weekly time frame. Changing the chart to the weekly timeframe, you would quickly see that the current levels are right at a strong resistance point. Three other times the stock has failed to push beyond these prices and has sold off aggressively.
Maybe this time will be different and will continue to push higher, but the weekly chart at least makes you aware of resistance that you may have not noticed.