A business intelligence tool pulls data from a source, does some arithmetic with it and puts the result on a screen. Charts, tables, filters, a dashboard you share with your team.
The tool usually stores nothing itself. It sends a query to your warehouse or your ad account and draws whatever comes back. That is why two dashboards side by side can disagree: they ask the same source a different question.
For a marketing team the question is rarely whether you need a BI tool. The question is which one, and what you put underneath it.