When working on an assessment template, you can specify an asset type to associate with it. This ensures that users selecting the template for assessments can select and evaluate assets of only the specified asset type or its subtypes. If a template doesn't have an asset type, users selecting the template for assessments can't select an asset. Instead, they are prompted to enter a description of what they want to assess.
Even if a template has an asset type, users can choose not to select any asset for an assessment. If an assessment without an asset is submitted, the Assessment Review asset that is subsequently created in Collibra does not have a relation to an underlying asset.