This “existence at a defined time & period” is particularly useful with long timelines when You have markers well out of sight on a timeline. The element is always available the user just simply defines the “in-out” points; it exists in discrete chunks wherever spec’d. This approach makes handling complex projects (long timelines with lots of elements) far easier.
I’ve had to adapt to Hype’s workflow but it is clunky in comparison to a motion graphics/video interface.
Below is a screenshot of a timeline from Apple’s “Motion” app. The “bars” for each element (layers in the timeline) define its appearance and exit (aka “in” & “out” points). No need to tell an element to be hidden before it is displayed - a much cleaner lucid expression of elements in a project. Note how each element is identified - not just in the list at the left but also on the bar itself. Filters, opacity settings, etc. are applied at the element’s bar, not in a separate “property” window~timeline.