Report Templates make it easier for you to get to the information you need. When you Build a New Report, you select the module you want to report on and then the report type, as pictured.
Then, instead of immediately being taken to a report builder where you choose filters and settings manually, you are presented with a set of report templates with the most commonly used filter combinations for each report type.
From this list of report templates, you can either click 'Build' to go to the report builder and add additional filters and settings, or click 'Preview' to go straight to a preview of the chosen report template.
You can still build custom reports for ALL items by selecting 'All Tasks', for example - always at the top of the list of templates - and clicking 'Build'. This will take you to a report builder with no filters or other settings applied, so that you can build your report from scratch.