Obviously, these builds are showing up more frequently because Microsoft is preparing for the RTM of Windows 10 version 1903. In fact, it's entirely possible that this is a release candidate, even though there are still some known issues.
Today's build includes a single fix:
We fixed an issue resulting in the Connect app crashing on launch for some Insiders.
We fixed the issue with Microsoft Store app upates not automatically installing.
Update: Microsoft has added a second fix to the list.
And as mentioned earlier, there are some known issues:
Microsoft Store app updates do not automatically install on 18356+. As a workaround, you can manually check for, and install updates via the Microsoft Store app. Open Select “…” > “Downloads and updates” > “Get updates”.
Launching games that use anti-cheat software may trigger a bugcheck (GSOD).
Creative X-Fi sound cards are not functioning properly. We are partnering with Creative to resolve this issue.
Some Realtek SD card readers are not functioning properly. We are investigating the issue.
If you install any of the recent builds from the Fast ring and switch to the Slow ring, optional content such as enabling developer mode will fail. You will have to remain in the Fast ring to add/install/enable optional content. This is because optional content will only install on builds approved for specific rings.
Most of these known issues don't seem like dealbreakers for an RTM build. The GSOD issue that happens when you run a game that uses anti-cheat software needs a third-party fix, and everything else can be serviced with a cumulative update.
Once we do see an RTM build, it will be promoted to the Slow ring and then the Release Preview ring, followed by a public release in April.