For VMware Cloud Foundation, you are correct there are two XLS workbooks so let me explain a bit about them both.
Planning and Preparation Workbook
This workbook is used to capture all the inputs used across the Management Domain, a VI Workload Domain and any VMware Validated Solution later deployed on top of VMware Cloud Foundation, the basic idea is capture the data once and then reuse where needed as you walk through the deployment steps as the workbook includes output worksheets based on the thing your building which align to the procedures in the documenation (example: DNS, NTP settings this are needed for pretty much everything). My colleague Ken Gould wrote a blog a while back (even if it's a little outdated now) which is worth a read which explains more detail around the workbook.
Once completed this workbook can be used as part of your infrastructure documentation, like an as-built document.
Deployment Parameter Workbook
This workbook relates to the vcf-ems-deployment-parameter.xlsx document you mentioned, and its sole purpose is to define the parameters required to perform bringup of the Management Domain. If you have captured your data in the Planning and Preparation Workbook already then you can transfer this into the relevant cells of this workbook.
Essentially what then happens is when you upload the vcf-ems-deployment-parameter.xlsx to VMware Cloud Builder, the appliance reads the xlsx file and converts the data into a JSON specification which is then used to execute the validation and deployment of the Management Domain which configures ESXi, and deploys and configures vCenter Server, NSX Management Cluster and SDDC Manager.
The alternative here would be for you to manually create the JSON specification file yourself using the API documentation but this is error prone and so the workbook helps minimise such issues.
