Well you're not forced to use it, but here's why it's always a good idea to install a child theme.
Unlike some themes where there are various flashy child themes built on top of a framework theme, the Beaver Builder child theme that's available for download on your My Account page is blank.
Why blank, and if so, why do you need it?
So that any code customizations you make don't get overwritten by updated versions of the parent theme.
See this WordPress Codex article for more information about why to use child themes. WordPress has instructions for creating a blank child theme, but we've made it easy by creating one for you to download and install.