The Connections filter group in the Impact Analysis - DB tab consists of a checkbox list with search filter:

With this filter, you can limit the displayed BI data to the nodes which are provided by the selected connection(s).

There is a special item on the list: !UNBOUND!. It stands for the database objects that have some SQL code not linked with any connection, i. e. "orphaned" SQL code.

As you noticed, there is a Connection filter group in CMS Explorer too. You could also notice that in the Impact Analysis - DB tab you see less connections in the same environment. It is normal as this tab shows only those database objects that are used by your reports.

Start typing a connection name you are looking for in the search control, and the list will be limited to connections that contain your input.

Tip
To determine connection(s) for the selected document, apply the View Relationships command in CMS Explorer to this document.

 

There is an additional item (All) in the list of connections. Use it to toggle between all connections being selected and all  connections being unselected.

If all connections are selected, or none of them, then the Connections filter is not applied, and it does not limit the data displayed.

 

 
See also

Business Objects

Connections (CMS Explorer)