Hi Arnab, in UiPath studio Invoking Workflow and Templates both are used for Reusing UI Automation. Putting workflows together to create a new workflow automation is a helpful strategy when you have a complicated UI automation. You can create specific workflows then combine them later to perform as one complete automation.
Now the main difference between invoking workflows and templates is that by invoking a workflow, the changes you made in the current workflow would also modify the workflow that has been added. When creating complex UI Automation it is recommended to break it into smaller pieces that can be tested separately and then integrate them later in a bigger workflow.
While saving the workflow as a Template helps you preserve the original workflow file. So whatever modification you made in the template, no changes will be made in the original workflow. "Templates" are often used for creating small pieces of common automation that are reusable and applicable in multiple workflows. So you can use templates if the workflow does not change over time.