It depends.
Is the author any good?
Can he write a credible sex scene?
Is the story any good?
What is the author's intention with the story?
Is the sex relevant to the plot?
Are the characters interesting to me?
Am I in the right mood?
I have read stories where the sex is the story, more or less, both excellent and horrible stories.
I have read stories where the sex has enhanced, detracted or had little impact on the story.
I have read stories where there was too much or too little sex, or the timing in the story is wrong.
I have read stories where the sex was all right, I guess, just totally irrelevant to my preferences.
IMHO there can be no hard or fast rules as to sex in a story.
But if you go to Nifty, or here, to read stories, you have no right to complain that there is sex in a story...
If you don't like a story, or an author, you do however have every right to vote with your feet (or mouse).