Is the directory business profitable? + Share some really good directories

Over the past year, I've noticed how makers have taken to creating directories on a large scale.

Since I am also thinking of creating one, I would like to know from owners or people who have experience:

• Do directories bring any significant profit? (approximate numbers would help)

• How do you monetise them?

• Can you share good examples?

I know it can be good for many reasons (SEO, affiliates, visibility, thriftiness—everything in one place, etc.) and I am considering it, but I also keep in mind that it can be a bubble, that I can be late, and that it may not be as profitable as it seems.

Do not want to end up burning money and time on administration so much. 😀