I saw an annoying spam and I wanted to use the report function and I was told that my email address will be revealed to the moderator when I report a spam.
Go on and make the report, if you care so much about your privacy, you can use a throw-away email for the forum (email not associated to your work or personal information).
I was temporarily deterred.
I think this is the main reason of revealing emails so that only valid forum users will be reporting. Without email collection, there could be frivolous reports or even a bot attack on the reporting system in order to mare it.
Am I going to be receiving emails from a moderator as a follow up for a report I made?
No, according to Charles-Tim. Moderators don't have such a time to be sending you emails.
What's the essence of revealing my email?
If there's any other reasons, a moderator can help us.