Quick notes on Salesforce dashboards and reports
Dashboards can have up to three filters. Filters can have up to 50 options. Ten are enabled by default. Contact Salesforce to increase this limit – Source
Great way to report at the ultimate parent level; create a formula field on the Account object which returns the top level (ultimate) parent. This can then be used as the filter criteria in reports to show activities, opportunities, etc across all account hierarchy levels for the given top parent name. Source 1 & Source 2 – Third formula
Dashboard filters can be based on custom text fields. Sometimes a custom text field does not appear as a filter option. There is apparently an issue with using one in combination with other filters where the underlying data type is not the same (underlying reports refer to a common filter field where these fields are of different types). Source
For Joined report cross block formula percentages use the Block designator for e.g. B0#RowCount/B1#RowCount
In Lightning Reports, reports grouped by row and column (matrix reports) will not show details if there are more than 2000 records returned
In Lightning Reports, you can’t reorder or add new columns while in summary mode with Show Details switched off
When converting a report definition that includes an outer join (with or without child records) any existing reports using that report will fail if the report has filter logic which includes an OR clause.