It depends! If you are only using a child theme to add code to functions.php and additional CSS to style.css, then you could quite easily replace your child theme with this plugin.

However, if you are using advanced templating features, such as replacing and updating different templates, then this is a situation where using a child theme is a good choice. You can always use Code Snippets as well for snippets, scripts and styles that are independent of your theme – it doesn't need to be a choice between the two.

Of course, if you do decide to use a child theme, then you need to make sure you are constantly keeping it updated as the parent theme releases new versions. This is one advantage Code Snippets has – snippets are stored completely independently of the theme ad other plugins, and won't be affected by those sorts of upgrades.