I'll admit that reporting design is my weakest skillset (at least in the data realm) - so I had to evolve a framework that myself + the team could easily follow.

How we design report pages:

1. Perspective: What changed, and is it good or bad?  This is often delivered via scorecards or a simple table.

2. Drilldown: What segments or cuts can we explore that drove that change?  This is where pivot tables with expand-collapse + filter-on-click come into play.

3. Action: Line-level details (usually in a table), that someone can take action on (ie this specific campaign needs adjusting, this specific landing page is performing well and should be boosted, etc)