It does exactly what you might imagine it does.
Nintendo has released Update 5.1.0 for the Switch, which- well, you know what it does. Years and years of similar updates for the 3DS and PS4 should have prepared you for what is coming: yes, it’s a stability update! Bring out the party hats, everyone!
No, but seriously, there are no changes whatsoever that are front facing or will be noticed by an end user. Behind the scenes, it sounds like Nintendo is patching up quite a few of the security exploits in the hardware, to make hackers’ lives as difficult as they can- while a new hardware variant that blocks exploits at a hardware level is on the way, I suppose Nintendo wants to do what it can in the meanwhile to keep things as tightly secure as possible on the existing model.
You can find full notes for the update for yourself below. Meanwhile, I hope that a new major firmware update is on the way soon- there are still some features the Switch is lacking that it could stand to have added to it.
Improvements Included in Version 5.1.0 (Distributed 5/30/2018)
General system stability improvements to enhance the user’s experience