This kind of fanfiction could potentially explore Hermione's curiosity or it might be used to develop a complex plot around her character's exploration of different aspects of sexuality. But it really depends on the specific story and the author's imagination.
The first appearance of lesbian porn stories online is difficult to determine precisely. It likely occurred gradually as the internet grew and different types of content became available, without a clear-cut beginning.
One strong muscle boy story could be about a young boy who was bullied at school for being weak. He decided to start working out religiously. He lifted weights, did bodyweight exercises, and followed a strict diet. After months of hard work, he not only built an impressive physique but also gained the confidence to stand up to the bullies. His story inspired many of his classmates to also take up fitness.
One benefit is better health. A Muscle Mom is likely to have more energy to take care of her family. For example, she can easily carry groceries and kids without getting tired quickly.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.