The main difference may be in the range of meanings. In a scale of 0 to 10 where "bad" is 0, one side will take "not bad" as a 4~5 while the other side meant i

The main difference may be in the range of meanings. In a scale of 0 to 10 where "bad" is 0, one side will take "not bad" as a 4~5 while the other side meant it as 7~8.