Dashboard filters allow you to filter all the reports in the dashboard at once. So rather than creating the same custom report multiple times, you can add the report to the dashboard and then apply a dashboard filter.
For example if you want to start every report the same key metrics table, you can create a single key metrics report and save it. Once you've added it to your individual brand report, you can apply a dashboard level filter for that specific brand. This means you don't have to keep recreating the same custom reports for every brand.
Dashboard level filters can be added at the top of the page under the title.