What is the purpose of using "<>"&"" In a Formula?

What is the purpose of using "<>"&""[/B] In a Formula?, this is the formula

=IFERROR((COUNTIFS('Interface Dashboard'!$E$10:$E$76,A4,'Interface Dashboard'!$L$10:$L$76,"Complete")+COUNTIFS('Interface Dashboard'!$E$10:$E$76,A4,'Interface Dashboard'!$L$10:$L$76,"N/A"))/COUNTIFS('Interface Dashboard'!$E$10:$E$76,A4,'Interface Dashboard'!$L$10:$L$76,"<>"&"",0)

This formula is pulling counts off of another sheet titled Interface DAshboard, and looking up Client Name in column E, with critieria's "Complete", and "N/A", but why the reason for using
"<>"&"", as a critieria, when there are two other critierias of "InProgress" and the "Not Started",