advantages of using child themes

Hi,
What are the advantages of using child themes? Is it best to use them instead of a parent theme? I need to make some major modifications to a site and it was recommended to create a child theme. Site is: aficreditsolutions.com. It was recommended that I use this plugin:
https://wordpress.org/plugins/child-theme-configurator/

Are there any downsides to using a child theme? What about when theme updates are available? How does that effect the child theme?