With Thrive Theme Builder, child theme no longer necessary. That's because Theme Builder is already fully visually customizable through the visual editor. You can change the design of any aspect of your theme simply by visually editing the theme templates.
Historically it was advisable to create a child theme in order to make visual adjustments to the parent theme.
So for 99% of users, there really is no need to create a child theme. You can just skip this altogether and go back to visually building your beautiful site.
For advanced users, however, creating a child theme can give you the freedom to extend the functionality with custom code. So if you have bespoke requirements that require extra coding logic.