While any extra plugin you add to your site will have some effect on overall performance, chances are that any change will be unnoticeable. The number of snippets you have on your site should make little difference, as they are all fetched in the same SQL query to ensure optimum efficiency.
If you are concerned about custom CSS and JavaScript snippets increasing page load times, we recommend you enable minification in the settings:
Please be aware that any CSS, HTML or JavaScripts code you load will need to be downloaded by the user's browser, and so will have an impact on speed. Make sure to only use what your project actually needs.