Ability to create Subchannels
Hierarchy is fundamental to organization. History is being made by each entry. Everyone should have access to an overview but may need the ability to focus. Imagine a factory with 4 Lines running 25 machines apiece. A four channel system is going to be tough to tease out historical information on a single machine unless tedious protocol is taken in every post by every team member. A 100 channel system naming every machine gives you granularity but becomes a scrolling headache.
Yves Basquet commented
Here as well the nature of our business is to have nested channels:
1) we create one channel per release/sprint,
2) we would need to create subchannels within that release/sprint channel, each for the various items that conform the release/sprint.