How is it calculated?
If Team A makes 180 runs in 20 overs, and bowls out Team B for 110 in 11 overs, will it have a NRR of -1? (9 minus 10)
If Team C makes 180 runs in 20 overs and Team D makes 160/5 in 20 overs, will it have NRR of +1?
In that case don't you think Team A is made to suffer because it suceeded in getting wickets and won much more convincingly than Team C?