All Scrum Team Members, including the ScrumMaster and Product Owner, should understand the high-level business aspects of the product that is being built. As well, that understanding should be solid enough, that it can be communicated to other people. This understanding helps the team members in many situations dealing with each other and with stakeholders. Understanding the purpose of the system is an aspect of both Focus and Transparency. This is essential for maintaining overall quality of the product. Development should always be done in a way that moves the system towards fulfillment of its intended purpose. If team members do not know their product in this way, it can cause significant problems in communication and in how Product Backlog Items are implemented. Finally, and perhaps most importantly, understanding the overall purpose of work is critical for a team to become a high-performance team. Without knowledge of this purpose, a high-performance team is impossible.
Scrum Teams work on one product at a time. The Product Backlog represents all of the work that needs to be done on that single product. The complete list of Product Backlog Items represents the goal of delivering all of the presently known features of a product. Multiple teams working on a single product, therefore, work from a single, shared Product Backlog. Working on Product Backlog Items from multiple Products causes the team to task switch into a different business domain and possibly into a different technical domain. Task switching creates wasted mental effort and therefore causes a team to be less effective than they could otherwise be. Having a single product to work on creates focus in both the business and technical domains.