Hide field for creating new objects setting
The setting Hide field for creating new objects (tasks or contacts) in the Planner list settings controls whether or not there's a special field in the list for quickly creating an object:
If this setting is not activated (by default it isn't) the field for quickly creating an object will be displayed at the top of the list:
If this setting is activated, the field will not be displayed. This lets you limit the ways in which users can add tasks and contacts, and it also helps save space on the screen.