Question about signed addition

using the circuit sub-adder, I am able to sum or subtract two strings in 2’s complement representation. my questions are: the sum that is the output of the circuit also represented in two’s complement?
2. what is the purpose of the negative flag bit if the sum is already represented in 2’s complement?

  1. yes (with the exception of overflow)
  2. it is not really necessary but it is comfortable to use it