Ques. about sheet reference in a forumla

I have question about why would you put a sheet reference in a forumla to have it reference the same sheet
the formula is on?

Hope I said that right.

Heres the formula-
=IF($P1.B6="";0;IF(SUM(C6:E6)=0;"--";SUM(C6:E6)))

this is the part I'm not sure about $P1.B6
Why would you need the $P1 (which is refering to sheet P1) when the formula is on the same sheet?

when this would work as well
=IF(B6="";0;IF(SUM(C6:E6)=0;"--";SUM(C6:E6)))

would there be a advantage to having the sheet reference?