Granted about the direct and indirect expenses associated with trading. But my point is, jobbing is a trading technique, also associated with high frequency trades. As I said, consider a scenario where your direct trading cost is 2 paisa... won't it be worthwhile to trade for one tick i.e. 5 paisa ??. With sufficient volumes, even 4-5 such trades in a session can give decent returns.
Combined with longer term trades, the whole thing can be really profitable.