I am experimenting with creating a tooltip page by following the above article for a categorical value column. It is working fine.
However, it continues working even if I remove the categorical column from the Visualization pane's Tooltip section.
So I want to ask - What is the purpose of Tooltip section in the Visualization pane?
The purpose of the field(s) used in that Drag tooltip fields here section is for the default setting of every visual on your source pages (that shows Tooltips properties).
By default on each visual (e.g. a table), if the Tooltips property section is turned on, a default setting is Page = Auto. In that scenario, Power BI uses the fields loaded into the Drag tooltip fields here section for every Tooltip page, to find candidate tooltip pages to show.
For your scenario to be still working, you must have specified the Tooltip / Page on your source visual.
FWIW I prefer to make those specifications on each source visual, to be explicit about what tooltip they should show. To leave Page = Auto invites any future Tooltip page to start appearing as an option, which might confuse the audience.
