Before addressing this question, it's important to understand how SSO works.
When SSO is enabled, users can log in to different applications and services using a single username and password. This technology eliminates the need to remember multiple passwords for each service, simplifying the login process.
Ease of authentication
SSO facilitates authentication. It is in fact a 2nd access channel, in addition to the email/password login, enabling access to your Klaxoon account.
If SSO is not forced, i.e. if users can choose their authentication mode, they will be able to use their password.
The administrator can impose this single authentication method by forcing SSO.
If you'd like to make SSO authentication compulsory, see this article: What is forced SSO?