It can be dedicated to a single service (or a full OS), runs a real BSD kernel, and provides strong isolation.
Overall, it fits into the "VM is the new container" vision.
Disclaimer: I'm following iMil through his twitch streams (the developer of smolBSD and a contributor to NetBSD) and I truly love what he his doing. I haven't actually used smolBSD in production myself since I don't have a need for it (but I participated in his live streams by installing and running his previews), and my answer might be somewhat off-topic.
More here <https://hn.algolia.com/?q=smolbsd>