[Voltus] set_pg_library_mode command option -power_pins?

Hi,

im using voltus for power grid view generation, what does the "-power_pins" option inside the set_pg_library_mode command do exactly? 

for example,

set_pg_library_mode \

    -celltype macros  \

    -extraction_tech_file <dir> \

     -power_pins { vdd 1.98 }\ ... 

is the voltage value 1.98 here for vdd important? by default, it will be set to 1.2, so i guess it is not important to set it to correct value or when i don't know what value to set it to?

thanks in advance