This feature is a lifesaver for fediverse. It allows you to see from a general perspective, reduces confusion and creates a more organized forum environment. Thank you to everyone who has already used this feature and I highly recommend everyone to use it.
It doesn’t combine them (because different people are subbed to different communities, although what you bring up has been discussed on the github for a while). The biggest thing though is discoverability, where your post is shown in multiple communities easily. Another added benefit is that there are less duplicated posts, your app/device can see that it was crossposted and show you only one in your feed rather than 3,5, 10 duplicate posts (and then you can tab between them)
How many apps support this though? My preferred one certainly doesn’t.