Do it make any difference having the following equation:

=($I4=$G$4)*SUMPRODUCT(--($I4-$G$4:$G4=0),(INDIRECT("R"&1044-$A4)):$R$1043,$C$3:$C3)+($I4$G$4)*SUMPRODUCT(($I4-$G$3:$G4),--($I4-$G$3:$G40),--($G$4:$G5-$I40),(INDIRECT("R"&1044-$A4-1)):$R$1043)+($I4<$G$4)*($I4*(INDIRECT("R"&1044-$A4-1)))

In one cell - or three cells defined below?
=($I4=$G$4)*SUMPRODUCT(--($I4-$G$4:$G4=0),(INDIRECT("R"&1044-$A4)):$R$1043,$C$3:$C3)

+($I4$G$4)*SUMPRODUCT(($I4-$G$3:$G4),--($I4-$G$3:$G40),--($G$4:$G5-$I40),(INDIRECT("R"&1044-$A4-1)):$R$1043)

+($I4<$G$4)*($I4*(INDIRECT("R"&1044-$A4-1)))

I think that for auditing purposes three cells would be easier - but did not
know if there would be any other advantage splitting the equation up into
three cells - and then combining the answer.

Note the equation could be copied down 2600 times.