I wasn;t exactly what i have in mind, but you indeed gave me a enlightened answer, which i haven't thought about it.
"The ecommerce shopping cart associates shopping basket contents with an ecommerce sesssion_id, which is kept for the entire transaction. ec_user_sessions stores page views and searches for each session."
You just showed me how the whole transaction is held by session_id and ec_user_sessions. It means that those APIs, (and a few more i believe), are used to take care of the user navigaton through the whole purchasing process without the need of user registration.
So, depending of the company goals such as:
1. simplify the buying process to the buyers - we can handle the entire transaction only until the purchasing process is finished and the shipping/billing information is properly treated.
2. personalized purchasing process - we can hold all the information we want from the client, to build a strategic, secure and focused marketing plan.
Please, tell me if i am wrong on this perspective, or if you have more to add. Including about the insight you had...