When given an algebraic expression involving subtraction why is it best to rewrite the expression using addition before identifying the terms?

When given an algebraic expression involving subtraction why is it best to rewrite the expression using addition before identifying the terms is because you can consider the basic rule of operations such as the PEMDAS or simply the MDAS in computing and calculating equations. Hence Addition comes before Subtraction. For example given -3 + 5, you can arrange this set into a simpler one such as 5 – 3 = 2. You aim to have a positive sum rather than a negative value sum.  

If jon had $4.00 then takes away $2.25, then he should have $1.75 left. $4.00 - $2.25 = $1.75 hope this ; )