Development of experiments to optimize HPLC-MS procedure using 2D central composite full factorial design
FCC is a variant of a CCD design. It's usual to run your 2 factorial design first and establish which factors are relevant.  In your case, it won't matter so much but if you have 5 or more factors, it does.  The 2 factorial establishes your range with an upper and lower limit (+1 and -1). When you move to CCD,  you now have options. Using alpha of root 2 gives your "response surface design" orthogonality and rotatability, meaning, loosely, it is easier to analyse for variance in your model. The reason for varying alpha usually comes down to operational reasons e.g if a negative time or negative mass would result.  This is when a FCC might be used instead. If you ignored your coded +1 and -1, in effect your root 2 values would become your new +1 and - 1. The rationale for this is when a formula is generated to model each response,  the one using coded factors (set at +1 or -1) will indicate the relative influence of each factor, which the actual factor values will not do. The formula using coded values will not base it on your alpha value.