There are few Lightning report features available in Spring ’20 release. Here, you can build a report faster and more productive with Count unique value in report result, Turn Off Automatic Updates to the Report Preview and Attach Formatted Spreadsheets to Report Subscriptions.
Count Unique Values in Report Results
When you create an opportunity report, you can see how many distinct values your report returns with a unique count. Also, you can add unique values in Account name columns to see how many individual account values appear in the report.
Go to the Report tab -> Open your report -> Add a unique count of values for a field, in the column, Click Aero icon (As shown in the screenshot below) -> Show Unique count
Release Note – https://releasenotes.docs.salesforce.com/en-us/spring20/release-notes/rn_rd_reports_unique_count.htm
Turn Off Automatic Updates to the Report Preview to Edit Reports Faster
You want to edit report fast by turn off automatic preview updates. You can make multiple edits without waiting for the preview to refresh after each edit. If you want Preview your data, you can manually preview data, manually refresh the report preview.
Go to the Report tab -> Open your report -> To turn automatic preview updates on or off, flip the Update Preview Automatically switch on or off. When off, a message tells you whether the preview shows your most recent edits and provides the option to refresh the preview. When hiding recent edits, the preview turns gray.
To refresh out-of-date data, click Refresh (1). (As shown in the screenshot below)
The preview reloads to show your edits. (As shown in the screenshot below)
Attach Formatted Spreadsheets to Report Subscriptions
Attach a formatted spreadsheet is my favourite feature of Spring ’20 release. When a user subscribes to the report, this new option lets then choose to receive result as a formatted spreadsheet attached to the subscription email. This email itself includes high level report details, such as report name, run time and link back to the full report in salesforce. It does not include row-level record details, which are included in the spreadsheet instead.
Go to the Report tab -> Open Report -> Click Edit Subscribe -> Select Attach results as a formatted spreadsheet file -> and click Save. (As shown in the screenshot below)