A range bar shows the highest and lowest repeat measurement (after any explained outliers have been removed).
In this example, it looks as if the value of B is greater than A:
With range bars drawn, it is not possible to draw a conclusion that the data shows a real difference:
If the true value lies at the top of A's range bar and the bottom of B's range bar, the value of B could actually be less than A.
In this example, even if the true value lies at the top of A's range bar and the bottom of B's range bar, the value of B is still greater than A. It can be concluded that the data shows a real difference.
Data that is precise:
Precise data makes it easier to show a real difference in data. It is difficult to draw a conclusion about a real difference if the range of results is wide.