If Our Statistical Result Was Significant, What Is the Value

If our statistical result was significant, what is the value of calculating effect size?

A) A significant statistical test tells us that the IV had an effect, and the effect size tells us about the size of the significant effect.
B) Effect size tells us that the IV had an effect, and a significant statistical test tells us about the size of the significant effect.
C) Effect size tells us if we need to change our test from a one-tailed test to a two-tailed test.
D) If the statistical result was significant, you do not need to calculate effect size (the information is redundant) .