Concept

Let say for example, you have 5 power computers, And a project so big which require days to finish its works
Such as 3D Rendering, or Video transcoding, or Large data sorting.

Sure, You can keep vertical scaling, until it's too expensive to do it. when you hit the critical point.
You might considering horizontal scaling, which now you need a way to manage multiple computers

Use Blender For Example

Let say there is a video file needs to export to mp4 file, video length is near 1 hour and the scene contain VFX or fluid computing

In this case you can seperate the render to multiple fragment, 5 mins per .mp4 file
In the end, you output folder will contain multiple videos

During the renderering, you can tell multiple computers to render different timespan
Then combine them in the end