Multi cycle path trough combinatoric logic circuit

If your question was - why i need additional register between adders, when answer is to increase speed. In real design input number may achieve more than 32 inputs and each input could be more than 18bit width.

If Your question was - why i use adder as a separate component when answer is to simplify recursion realization, in this way a can easily pass through generic values. Maybe there are different ways of creating such designs, but i simply don't know them ;)

In this VHDL code i need only change generic values and Quartus II software generates required stages to sum all input values (tree shaped architecture). Input values can bee even or odd.