Netflix & account sharing; extra subs mandatory or not?

[kiddingguy]

So Netflix is sending out email to their customers regarding account sharing/users outside your household.

I've seen the mail. It's friendly and not stating that you are required/mandatory to purchase additional subscriptions. 

There is also no penalty mentioned, or blocking/account banning.

How should we look at this email? Is is mandatory [given the license & terms 'yes') or are they just friendly asking?