FB Ad Question

I am a certified Feminine Power Coach. The Feminine Power Fan Page on FB has 181,000 likes. I want to do some Facebook advertising to grow my business.

In all the FB ad courses I have seen they suggest targeting millions of people.

It seems to me my perfect clients are women that have liked that page, and that is obviously way more than enough people for me to work with.

Is there a reason to target a bigger group than the fans of the Feminine Power FB page?