The user macros are not expanded in calculated items.

For example:

• creating a virtual host
• definition of 2 macros {$HOST_MACRO1} et {$HOST_MACRO2} containing the names of known hosts zabbix
• application of a template with a calculated item defined as follows:
  last("{$HOST_MACRO1}:proc.num[snmpd]")+last("{$HOST_MACRO2}:proc.num[snmpd]")

This item goes unsupported and the error message tells me clearly that the macro is ignored:
Can not Evaluate function [last ()]: item [test {$HOST_MACRO1} proc.num [snmpd]] not found