Some people talk about fragmentation to support the idea that Elementary OS is well-covered on the SE network already.
When I asked people on eOS g+ why don't they go to SE, I got 2 comments:
That is, one cannot counter the aforementioned proposal on the grounds that there is enough eOS stuff on SE. There is NOT.
About "fragmentation" one should not be abused: better focus doesn't mean fragmentation. eOS is top 10 ditrowatch hit nowadays, and when you are dealing with a specific distro&community like eOS and you have the opportunity of having your own platform for that, why not take advantage?
ElementaryOS will go far and far away from Ubuntu, while eOS questions are offtopic on askubuntu; but anyway: askubuntu is not the issue here.
Concerning unix.stackexchange (Unix&Linux), it will become larger and larger as
- there are hundreads of linuxes and
- U&L is not just Linux, but also Unix, Mac included, although there is a Mac-specific SE area.
And the more U&L gets bigger, the bigger will be the need for special distros like eOS to have their own Q&A pages, with clear rules to remove off-topic questions and blabber, like SE has.
Saying that we don't need eOS-SE because we have U&L is like saying we don't need U&L because we have superuser.