Let’s say:
- I am on instance A.
 - I browse on a community that is on instance B
 - a user from instance C post something on that community B.
 
Now i want to share a link to this post. Which instance should i pick?
- A my home instance
 - B the community
 - C the post author
 


Id pick the communities instance because that’s the one responsible for federating the post and comments. Id only choose the instances a or c if b is or is planning to shutdown, or if I really wanted to show people what my home instance is