Stupid gun rules, like magazine size limitations, sure, but they almost never "come for my guns." Often the suggestions are perfectly reasonable in my mind - national gun registry, for example.
Another scenario - the FBI is monitoring radicalization in a small community. They check the gun registry to see which of the people in the community becoming radicalized are actual potential threats and zero in their investigation on those individuals, to prevent a shooting.
Etc. Basically just makes law enforcement's jobs more feasible.
The government doesn't have the resources to "confiscate" every registered gun owners' guns at the same time, and so we would be well aware if a confiscation by a tyrannical government is coming, and all of us weirdo militia folk and preppers would already be putting the sandbags out. Trust me, some of these guys are practically wishing for it.
Similarly, police who are serving an arrest warrant might be able to serve the warrant with the knowledge that person of interest has several firearms on the property. Sometimes police know this today, but not because of government records.
(I'm not arguing a personal position one way or the other, just explaining the rationale.)