Whatever form of communication that your team uses, it should be open and discoverable by all.
Pros
- Inclusiveness
- More ideas from more people
- Visibility of work
- Truely cross team collaborations
Cons
- Noise
- More ideas from more people - yes this is not always a good thing
Exceptions
There are legal and/or commercially sensitive reasons not to expose all converstaions to everyone. Private channels/conversations should be the exception rather than the rule.