If no tags are given to health check executor, currently all health checks are executed. This was reasonable when the health check module was created, but today typical setups include checks for tag spaces that do never make sense to run at the same time, e.g. a common setup used for a product based on Felix uses checks for tag "pre-upgrade" - if the system is altered to satisfy all those checks some other checks that check for "regular health" become CRITICAL. For this particular setup there is no system configuration that will return OK for all tags executed, and since this is confusing for novice users, for the case no tags are given all checks for the tag "default" shall be executed.
This is a new convention that has to be learned.