Facebook is letting users decide whether they want to receive emails from Facebook applications they subscribe to, similar to the opt-out option on other Facebook applications.
By default, the checkbox is selected so that users receive emails.
Now, email spam can be controlled by the user: If emails aren’t wanted, then simply turn off emails from that application.
An application may have legitimate needs, such as sending time sensitive reminders to a user.
For a deeper dive into Facebook’s policy around “spamminess” — whether in email or in Facebook’s notification section — here’s a description from a Facebook employee (Facebook login required).
[Disclosure: Doug Sherrets owns a small number of Facebook shares.]