Timeline in node based compositing
Usually, the workflow goes like this:


Capture your plates, real, cg, doesn't matter.
Hop into Nuke, composite your plates, then render each shot individually.
Edit the shot in your editing-software such as premiere.
When the final edit is done, re-import each individually rendered clip into a grading software such as Resolve, apply your color grading, export again and replace the ungraded file in your edit.


So just for pipeline-purposes, it's often inconvenient to use a timeline in compositors like Nuke.