If you're suggesting it has an effect on operations in other ways, then sure, I have no trouble believing that (shifting guests to a different park, changing park hopping patterns, etc.). But when people suggest that opening a new ride means there will suddenly be 20,000 more people in the park every day, that's just not true.
It may have been true at some point in the past, but Disney attendance is high throughout the year now -- and there haven't been any openings in the past decade that moved the attendance needle enough to outweigh the capacity addition.