Dry fire doesn't always help accuracy. It depends on what problems you are trying to fix. For some, it's not really of any use.
As for hampering accuracy, I have found it CAN be quite detrimental uner soe circumstances.
Namely shooting a DA/SA gun with a significant difference in trigger pull between DA ans SA, I found using DA all the time in dryfire had taught me to expect a 9lb trigger pull, and other than the first shot on a stage it was all really a 4lb SA pull. WHich reuslted in me shooting low or low-left a lot. Took me about a month to figure out what caused it, and about a month to break the habit.
For the M&P I cock it, first shot is real dryfire, the rest of the string of dryfire is just working the trigger without cocking it. With the longer pre-travel of the trigger job, it's the best analog of a stage I cna get dry-firing.