There are a number of possible ways that an investor could use the ETFs ranging from short-term tactical applications through to strategic, longer-term implementation.
Volatility:  active traders can capture and magnify intra-day moves
Swing-trading:  typically a short-term strategy, two to five days, where investors take positions in relation to an identified technical range
Hedging:  for investors who wish to hedge risk on a stock position, which they hold directly or through a third-party fund or index-tracking ETF
Event driven:  in a takeover situation, for example, an investor may go long the company being acquired and go short the acquiror
Relative value:  situations where an investor simultaneously runs a long and short position, which could be long a stock versus another stock or an index, or vice versa
Portfolio tilts:  an investor may look to overweight or underweight individual stock exposure to take advantage of the fact that index returns can be driven by a small number of stocks
Momentum:  magnify returns when stocks are driven by momentum
Long-term trends:  take positions in stocks that are at the forefront of technological or societal change with the scope to appreciate significantly over multi-year periods