It controls the layout of the meal list on the customer's Real Time page (Client Config, tab Theme: Kitchen):

• Yes (default): meals are grouped under category headings with a horizontal category bar that scrolls to each section; meals with no category go under an Uncategorized section, which is shown only if Show Uncategorized Meals is also Yes.
• No: meals are shown as one flat list of cards.

Only categories flagged to show as anchors ("Show On Anchor") are used for grouping — meals in a category that isn't flagged fall back into the Uncategorized bucket.