Any time a data source field is referenced by a block, that block will not render until all the referenced data sources are available.
Being available means that if the data source has never been used or has had a filter or sort order changed since it was last used, it will to be retrieved again by the app.
Occasionally you want to have a dependency on a data source that is not displayed by the block itself.
In every Block a field, "Other Dependencies" (under 'General Settings') can be used to express that dependency.
To do so, use the editor and insert a reference to any field in the data source, like "[[ds:/source/item/id]]". You may reference as many data sources as needed by placing an expressing referencing each one in this block.