when to use Date.[date] ?

Hi ilcaa72,

When you turn on time intelligence option, power bi will try to analysis your data value column as a hidden calendar.

These extend fields which you mentioned are from analysed hidden calendar, you can direct use these fields to get different date unit from date value without specific dax date functions.(year, month, day...)

It can help power bi analysis data and summarize records with different date level and provide support with dax time intelligence functions(such as YTD, MTD, PREVIOUSYEAR...), It can help you calculate and summy records with specific date filters more simply.

>>if my simple calculation, if i use this parameter, it either only shows zeros, or doesnt work at all, so i am trying to figure out when these should be used and hopefully explain why...

Notice, these extend date fields still not fully works with dax functions, some functions still need to use original column name to find out related values to calculate.

Reference links:

Time Intelligence in Power BI Desktop

Regards,

Xiaoxin Sheng