It ultimately depends on the test and also the risk profile you are as a user.
Some tests may be used as part of a regular health-check routine, while others are most useful after a specific event, possible exposure, new symptoms or a change in risk. For example, STD testing may be appropriate after a new sexual partner or unprotected sex, while tests such as PSA or colon health screening may be taken periodically depending on your age, risk factors and advice from a healthcare professional.
Testing more frequently is not always more useful, particularly where a condition has a window period and may not be detectable immediately. Always check the guidance on the individual product page and in the kit instructions. Speak to a healthcare professional if you are unsure how often to test or have ongoing symptoms or concerns.