Why is rendering nullified by moving a clip underneath?

[Pooch88]

See attached. clips are rendered & green - but by changing/moving a clip UNDER it, it becomes red again — why?

[Ann Bens · Accepted solution]

Why? Because the section is not rendered with all clips involved.

[Pooch88]

thank you, for your rreply. But why would PP consider a hidden clip when rendering?  it seems to me like clips underneath should have no effect on this (?)  what is the *practical* utility here?

[Peru Bob]

The software still needs to decide if it has any effect on the timeline, such as blending modes.