A disposable inbox can reduce the number of websites that know your primary email address. This can help separate one-time interactions from personal communication and reduce unwanted promotional messages. Privacy is still dependent on the temporary email provider, website logging, and the information you choose to submit, so avoid entering sensitive personal data into untrusted services.
For practical use, always review the provider rules and avoid sharing sensitive information through temporary inboxes. A temporary address is best suited to low-risk, short-term interactions.