The problem of SaaS is having your company data stored by someone you have to trust... So I reckon it depends on your use case: if I'm a small company who doesn't want to bother running/maintaining the service then I'm more than happy to hand it over to someone else and trust them. If I don't want to trust anyone with my data I'd rather have something simple to deploy and run myself.
The same way that having a closed client prevents you from customising it to fit your needs but can be helpful if you had no intention to do so in the first place.
Yeah, there'll always be companies like that but as more and more large orgs, government departments, etc. migrate all their email over to Gmail, I'm starting to consider that as a niche. Those orgs are also disproportionately likely to want to build their own thing because they have a hope of making the economics of scale add up.
True for big corps, although it's quite strange given they're usually the most paranoid ones on security.
But I was more thinking about techie SMBs to whom running a chat/collaboration server is not scary, better in terms of flexibility and cheaper than paying someone to handle it.
The same way that having a closed client prevents you from customising it to fit your needs but can be helpful if you had no intention to do so in the first place.