Google provides a useful CAPTCHA that can be used to provide better security for your pages, namely Google reCAPTCHA.
Fun fact: CAPTCHA means Completely Automated Public Turing test to tell Computers and Humans Apart.
Whenever an action in your Pimcore-project needs to be protected with Google reCAPTCHA V3.
If your site has some kind of authentication (e.g., login, registration, ...) or allows to submit product reviews, you'll want to include Google reCAPTCHA into your site as this will increase both trustworthiness and security. See Google's explanatory video for details.
Please note that there are some privacy concerns, as it is said (though, not proven) that Google may collect user data for their own benefits - other than Google reCAPTCHA improvements.