the experts have always said you pre-spray with a high Ph pre-spray then rinse with a neutralising solution such as F & F rinse to return the carpet or fabric to an acid side state.
now the 'experts' are rinsing with freshwater which is either neutral or can be slightly alkaline so what happened to the original neutralizing theory?
My opinion is remove the pre-spray not neutralise it, which is done with lots of flushing water.
so if you want ( and its safe to do so) use a high Ph pre-spray that's Ok but it's important that all the pre-spray is removed, then the subsequent Ph of the carpet is the Ph of the rinse.
I use Chemspec Enzall and rinse with Crftex woolsafe powder , so i leave carpets with a neutral Ph, although some detergent is left in the carpet not enough to have any residual harmful effect