Effective Odds?

[XxGodJrxX]

I just bought TOP a few days ago and started reading through it. I just finished the chapter on effective odds, and am extremely confused. Why should one calculate effective odds rather than just pot odds for each street? For example, there is a four flush after the flop and 5SB in the pot and am last to act. Pot odds would say that we should call here, so what would be the point of calculating effective odds as well?