Premium service is usually an improved version of a free given service. It is either a more expensive service than the basic one or a paid version of the free service (in this case, see the concept of freemium).
For example, advanced messaging services provide more storage capacity. The editing site can provide advanced access for archiving and ad-free access.
Business models based on quality service marketing can sometimes make it difficult to establish your position.
The concept of quality service is obviously very relevant and the term is often misused for marketing or commercial purposes.