It is kinda interesting to see the mastodon app ecosystem split into 2 groups:

a. those that follow hashtags (hence put all posts from those hashtags directly in the your main timeline);

b. those that pin hashtags (hence allow you to switch between hashtags without polluting your main timeline);

The official implementation is using type A, so some apps are taking advantage of these API; but I never got used to this style of following content, I am very much in the type B category.