Nintendo wants to send us chirpy emails telling us about current games, upcoming releases and so on, and part of signing up for a Nintendo Account is deciding whether to accept these promotional messages. Nintendo is so keen that we get these, in fact, that it's now giving out Platinum My Nintendo points for all that are signed up.
If you sign up for these emails you get a one-off 30 points, while you can get another 10 points every month if you stay signed up.
In general Nintendo doesn't get too carried away with these promotional emails, so for points chasers it's likely worth it.
For some, though, spam just isn't desirable - Nintendo may not get everyone in exchange for shiny points.
Yes, we're aware that Nintendo's emails aren't technically spam by the definition of the term, but any excuse for Monty Python videos is happily taken.