The Porn to Plot Ratio:

The main difference between erotica and other forms of literature is that the prose in erotica is intended to be sexually exciting or arousing to the reader. There is variation on the priorities the story takes, and if it explores scenarios other than erotic ones. Here is a scale that categorizes the prominence of pornographic material in your story. A higher number on the scale means the work includes more background elements other than sex. Please note that a higher score does not mean that the work is higher in quality. A low level story can be expertly written for its narrow purpose and a high level story can be a poorly written mess. This list isn't official categorization and meant as a suggestion only.

1. Porno: Stories at this level will be entirely focused on describing an act of sexual intercourse. Characters are no more than a physical description and possibly a name. The writer usually chooses to focus on sensory descriptions of the acts being performed and the bodies of the characters. There probably isn't even be pretense before they take off their clothes, after the sex is over the story will end.
2. Porn: Stories at this level have some sort of scenario for pretense, but quickly moves to the sex. Characters in these stories are often simplified archetypes such as the classic cliche of the babysitter and pizza man, they may have personality traits and reactions, but are ultimately just there to get it on. The story is still unlikely to continue after the sex scene.

The first two categories seem to be a lot more likely to appear in video form than as writing.

1. Erotica: Stories at this level are probably the most common on CHYOA. The premise of the story is still intended to enable the writing of sex scenes, often being clearly based on a kink or fetish, but there is a little focus on other aspects of writing. Characters might react to the scenarios they're in in a more varied way, and show more aspects of the lives they live outside of the sex. The story is likely to string multiple sexual encounters interspersed with less erotic chapters every so often to provide a break, and do some world-building or character development, but this development usually focuses on the sexual elements of the character or world, such as a world of sexy monster-girls.

2. Erotic Stories: Stories at this level are often hybridized with another genre, such as comedy or western. The premise of the story might not even need to emphasize the sex, and the characters are more might fit in with the classic archetypes found throughout literature, such as a no-nonsense gunslinger for a western, and go into depth about their time spent in that role. Explicit sexual themes and scenes are still included as a key part of the story, and the world-building and characterization touches upon sexual elements, but also goes into depth on other things. Very rarely, stories at this level have a little mainstream success for adult media. This is often found in the Sex Comedy genre in English speaking countries, or Ecchi in Japan.

3. Stories with sex: Stories at this level can be categorized entirely as another genre. Explicit sex occurs, and sex is a part of life for the characters, but the story is focused on the other aspects of the work for the majority of the time. Works at this level might find a broad mainstream appeal, and aren't often found on CHYOA, but are still meant for adults because of their content.