The dependent item page has this paragraph:

To allow for bulk metric collection and simultaneous use in several related items, Zabbix supports dependent items. Dependent items use the master item to collect their data simultaneously, in one query. A new value for the master item automatically populates the values of the dependent items.

While this is useful info and correct, the information about how/when dependent items is a bit hidden in that introductionary paragraph. It might be useful to move the update information to its own paragraph.

It would also be useful to explicitly state that dependent items cannot have different update intervals from the master item.