I wonder what amount of a service like Tumblr's server expenses are strictly related to storing and serving historical content, and what value it really brings

I wonder what amount of a service like Tumblr's server expenses are strictly related to storing and serving historical content, and what value it really brings to the business. What would a service like Tumblr look like if things just got deleted after 90 days, or a year? What would your server costs look like then? How much traffic do ancient posts actually garner, in aggregate? Could you monetize permanence (only pro users data is kept for longer than a year)?