Indicators or Order Flow?
Perhaps the best answer to this question is the Upstairs V. Downstairs Debate between Tom Baldwin (CBOT T-bond floor trader) and Peter Borish (#2 man for Paul Tudor Jones).
In short, trading systems tend to be longer term with larger draw-downs/risk/stops while trading Order Flow is reacting to what is moving the market now.

"... if I’m going to buy 900, I might as well buy all I can, it’s only going to be probably 1500 and in the process its going to move the market ..." "... the goal is to move the market as far as you can to a point where there can be a two-way trade [size] ..."
Tom Baldwin, T-Bond CBOT Floor Trader, Market Wizard