In a cricket match, a captain always wants his bowlers to give less runs and pick wickets in less over, and in all situation, and all format.
If one has to multiply LER x LSR you will get an X- Factor of your bowler.
Low Economy Rate ( aka Runs/Over)
Ideal bowler should have an economy rate of less than 4.50 runs in a ODI and less than 3.50 Runs in a Test match.
Low Scoring Rate (aka Strike Rate)
Ideally a bowler with a strike rate between 40/50 balls per wicket is an effective bowler.
Glen McGrath (Australia in Pakistan, 3- Test series, 1998)
Inns : 4
Overs (Balls) 120.5 (725)
Wickets : 12
L E R (R/O) = 344 / 120.5 = 2.84
L S R (St. Rate) = 725 / 12 = 60. 42
X – FACTOR = 2.84 x 60.42 = 172