Sentimentality can work against an author because it might cause readers to reject a story or its characters work against an author because it might cause readers to want more excitement or plot twists an author because it makes a plot more interesting an author because it makes a story more realistic

The definition of sentimentality is, the quality or state of being marked or governed by feeling, sensibility, or emotional idealism, especially to excess. So I would say  " it makes a plot more interesting help an author because it makes a story more realistic" I'm not 100% sure but it seems to make the most sense, have a nice day!