It was always required but not illegal. Which made it impractical but still an option not to do so. It wasn't uncommon for people living with their friend, partner or in a bad neighborhood to remain registered somewhere else. Now it is illegal and people actually get sentenced in court for living a month with their girlfriend without letting the government know. And it is already being selectively enforced against those the government doesn't like but can't prosecute for something else.

You might not like it but it is true. Finland had a plan to join NATO in case they felt they had to. And when that happened they had plenty of political and public debates and support. Sweden's plan was to cooperate with Finland. In the declaration of government from late last year it was declared that Sweden shouldn't join NATO. So when Finland wanted to join NATO Sweden no longer had a plan and therefor without convincing debate or support also requested to join NATO.

This is important because laws, policy and principles aren't worth much if you can quickly change them. Sweden has shown itself capable of changing fundamental things if it is sufficiently freaked out. And to do so without much resistance or recourse. As Sweden had no alternatives, and with many even stating so publicly, it also isn't in much of a position to resist demands from the US or other countries like long standing members would. It is likely that Sweden will become a "Nine Eyes" country like Denmark which has resulted in numerous incidents for them in recent years.

And these are not the only examples. It's everything from Swedish police using teargas for the first time in history with barely anyone noticing to not being able to publish scenic drone footage without approval.