The smallest team license contains a license key for up to 5 users. This is because there is, in almost every case, at least one person creating Power BI reports and at least another one viewing them. Furthermore, reports are usually shared with an even larger audience in your company which is why our minimum required number is 5.
As we do not differentiate between Power BI report designers/creators and report viewers, it is required that every single user that engages with Power BI reports using our visuals is covered with a license. For more information about licensing, visit this article.