Nintendo recently offered up Switch firmware 3.0.1, and as usual, no big details were given on why the patch was issued. Turns out hardware hackers have sniffed out the reasoning, and it was related to a huge exploit.
Prior to 3.0.1, the service manager ("sm") built-in system module treats a user as though it has full permissions if the user creates a new "sm:" port session but bypasses initialization. In 3.0.1, "sm" returns error code 0x415 if Initialize has not been called yet.
What does all this mean? Turns out the issue allowed full permissions to any service in the OS for anyone. This one issue is going to be the key to homebrew on the Switch. Obviously Nintendo wants to stop that, which is why they've released the update.