Perhaps for a large company with multiple offices etc, sure.
For a smaller company though, other than as a search tool (previously asked questions) I don't see what advantage it has over just using Slack/Teams etc. in a relevant channel to your question.
Because even in a small company, searching past content and conversations in Slack is a pain. The information gets lost. There is no reference back, so people just end up asking the same questions again, which is both super annoying and a gigantic waste of time.
I mean, I assume that they don't actually care about small companies, they don't have much money anyways. In these scenarios, they tend to act as a "loss-leader" for marketing purposes, mostly.
FWIW Atlassian's perspective is generally more like "they don't have much money yet, so let's get them while it's easy to get them". Small companies grow into big companies, and small single-team deployments tend to spread into big whole-company deployments - but small customers are much easier to get than large customers :)
Disclaimer: long time Atlassian employee but all words are my own.
Yes, companies large enough where you might not know who you'd need for help with a problem within your first week is exactly the use where SO shines, in my opinion.
For a smaller company though, other than as a search tool (previously asked questions) I don't see what advantage it has over just using Slack/Teams etc. in a relevant channel to your question.