Does using a condom only some of the time offer any protection from STIs, including HIV?

Condoms are only able to protect against STIs when they are in use. Therefore, using condoms some of the time , means you are only protected some of the time. It's suggested that every time you have a new sexual partner that you get tested. If you and your partner are both STI-free and promise to see each other exclusively then you can have condom-free sex without worry of getting an STI, although then there is risk of pregnancy. Using a condom always is still the safest option.