Manual Navigation temporarily disables the Auto ... features of the Controller window and allows you to control track expanding, collapsing, selection, and scrolling explicitly.
You can use Auto Expand, Auto Select, and Auto Scroll to determine the overall behavior of tracks in Track View. However, in cases where many animated objects are selected in the scene, this can cause unwanted behavior such as abrupt scrolling or too much information appearing. Turning on Manual Navigation temporarily disables these settings so that you can expand/collapse tracks, select tracks, and scroll as you see fit. However, the Auto ... settings are retained and restored as soon as you turn off Manual Navigation.
When Manual Navigation is engaged, buttons appear in the Controller window that allow you to expand or collapse individual parent tracks such as objects or materials.
To collapse and expand individual components in the Controller window:
A small, circled minus or plus sign appears to the left of each collapsible and expandable item, respectively, in the Hierarchy list, such as Position and Rotation tracks.
The track collapses or expands, and the opposite symbol appears within the circle.
When Manual Navigation is off, tracks expand based on Auto-Expand choices made on the Show menu Auto Expand submenu.