So I don't see consensus here. What if my served data ist "variable data"? An no distinction between man made or machine made is given here. Also this might not be flexible enough for some scenarios.
Is the data being stored customer facing or internal to the machine?
That's the rule of thumb I see applied to what goes in /srv. In a LAMP box for example I'd expect to see the website(and site logs), database files, and POP3/IMAP spools stored in srv directories. Machine specific data like system logs and email processing spools get stored in /var.