When to Update FME?

So you have been using FME for a few years and everything is great. But how long can that last. When should you completely rewrite a workspace and when should you only upgrade? Here are a few guidelines and examples.
Presentation Details

Presenters:
Michael Baer

Presenter Company:
Saint Louis County MO

Event:
FME World Tour 2018

Industry:
Software/Technology