There are several factors to consider when deciding which tests to automate, including the importance of the feature to the overall application viability, whether the test is redundant and already covered by other automated tests, and the potential impact on build time and maintenance costs. Automating all tests may not be feasible or cost-effective due to the overhead in design and development, as well as the need for ongoing maintenance and adjustments when features change. A balanced approach that prioritizes automation for critical features and manual testing for less important ones is recommended, taking into account the benefits of automation, such as quick bug detection and reduced human error, against the potential drawbacks, including increased maintenance costs and redundancy issues.