When casual movie goers decide what movie they're going to see, its usually based off word of mouth. RT ratings create word of mouth indirectly.
At the end of the day people will always go by what they hear from other sources. We all do the same thing. (In my case, I look for reasons not to go see DC movies
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Most of the audience consist of casual folks. You can't deny the influence of RT. If it wasn't that big of a deal, DC wouldn't have blocked the rating.
Movie studios use RT scores now to help PROMOTE their product if the score is "fresh". You many not agree with it, but its affective none the less. People only seem to hate RT when a movie they were anticipating gets a low score.