It reports an interesting article found online regarding user management of power bi connected to Tabular .

With the latest release in fact, you can download the Enterprise Gateway that connects the power bi instance directly to different data sources including service Tabular Analysis

When you publish any given source of powerbi to update the data you must define an account for the gateway , it  allows you to connect power bi same to its source data .

The problem is that, use an account with excessive permissions (or even Administrator ) could allow users to access sensitive data that should not have access (think sql server) .The solution is usually to use a specific user than minimize the ‘ data access .

But when you use SSAS to be careful because power bi for access to SSAS uses the effective user name as access, the user that fits the gateway serves only to make the initial access analysis services .

To access the account that uses the gateway must be an administrator of SSAS , if a different user is entered , the system is unable to use the effective user and an error message .

For mor info Power BI & SSAS

SSAS employs the EffectiveUserName feature to provide fine grained permissions to data in the model.

With EffectiveUserName, the proxy account is used only to establish the initial connection to the SSAS server, and all queries are executed with the permissions of the consuming user, allowing the data to be security trimmed.