There is a display hierarchy, in that display must be enabled at a higher level to reveal display settings at lower levels. Toggling the top level, model display, is convenient for hiding and showing an entire model without disrupting its detailed appearance. Whether there are lower levels depends on the type of model:
Although turning on display at a higher level reveals display status at a lower level, it does not change it. For example, turning on model-level display will not show atoms with individual display turned off.
See also: show, cartoon, surface, rename, Model Panel