Zabbix agent supports "-p" or "--print" option to print the list of supported items:
This is useful for manual execution, but for automated parsing it might be useful to omit the values. One example use case might be Zabbix bash completion, see https://github.com/zabbix/zabbix-bash-completion .
Printing values (e.g., for web.page.get above) makes it harder to parse item keys out of that list. Also, there are potential problems when item values are expensive to obtain, give errors or that simply hang with default parameters.