It's not a weekend trip but a round-the-clock job with many responsibilities that includes a lot of chores, repairs, maintenance and experimentation. The main value of this is the research that can only be done in a microgravity environment. You can search all the experiments that have been carried out onboard on this site.

Here are the categories of their research straight from the page:

Biology and Biotechnology: In microgravity, controls on the directionality and geometry of cell and tissue growth can be dramatically different to those on Earth.
Earth and Space Science: The presence of the space station in low-Earth orbit provides a unique vantage point for collecting Earth and space science data.
Educational Activities: The space station provides a unique platform for inspiring students to excel in mathematics and science.
Human Research: The space station is being used to study the risks to human health that are inherent in space exploration.
Physical Science: This unique microgravity environment allows different physical properties to dominate systems, and these have been harnessed for a wide variety of applications.
Technology: Studies on the space station can test a variety of technologies, systems, and materials that will be needed for future long-duration exploration missions.

One of the many discoveries that hit the front news includes the lengthening and shortening of human telomeres in microgravity and after returning to Earth, as well as the gradual bone density and muscle loss that could prove challenging in long space missions. They've also discovered how bacteria become immune faster to antibiotics in microgravity. There many physics demonstrations on YouTube of everyday phenomena like how fire behaves without gravity and how gyroscopes serve as an anchoring mechanism in space. They've also developed many incredible technologies like the full recycling of urine into drinkable water. Discovered how some bacteria are able to grow outside the craft and how tardigrades are incredibly resistant creatures to extreme conditions, and whose properties could help solve questions about the spread of life around the universe. They've also developed methods to grow plants in space. The setup they have up there may yield results for agriculture in general. And the list goes on without even mentioning the trickling developments that impact other industries that have made history.