When creating a new dashboard, I see an option for using a template, what is this?   

A template is a set of viewlets that are opened automatically when the dashboard is created.   For example, you might want queues and topics only or you would prefer managers too.  To do this, you use a template.  In order to create templates, you need to be an authorized user (Use Dashboard As Template role).   If you have this right, you can create dashboard templates which are shared with other users.  This is done by right clicking on the dashboard and selecting Set as default template

From that point on, when anyone creates a new dashboard, they could select this as the template

You can create different templates for MQ, EMS and Kafka and they will show up only when that product is selected.   

Also, note that the node and queue manager default to match the template, but can be changed.   That way, you can create different dashboards for different managers using the same template.