Google has finally started the process of migrating Nest accounts to Google, and there's no going back after you merge. So, you ought to give it full consideration before proceeding. Something to consider is that Google will "democratize" your Nest products when you migrate. All family members can add and remove people from the home. They can even remove you.
Google decided to allow migration from Nest accounts to Google after several embarrassing security snafus. With Google, you get advanced 2FA, suspicious login detection, and more. It makes your home security devices more secure, which only makes sense. However, your account post-merger relies on the Google Home app for user management, and that means home members have a lot more power. As Google points out during the migration, anyone you add as a home member can remove you (or anyone else) from the home at any time. The sole exception is Home Entry Only access, which is still managed in the Nest app—those people only have PIN codes for using your lock or security system.
Previously, no one could remove the "owner" in the Nest account. After migrating, the Nest app will still list you as the owner, but the Home app doesn't make that distinction. If someone removes you from the home, all your Nest devices will disconnect from the account. We reached out to Google to confirm this is as weird as it sounds, and indeed it is. Here's the statement.
As part of the migration we wanted to allow all family members of a home to have equal rights to the home. In a sense we wanted to democratize Nest products in the home, for example a husband and wife should both be able to control their home equally. We are very explicit to migrating Nest home-owners about this change which is necessary to migrate to a Google Account, and encourage users to be thoughtful about who they add as family members.
This has always been the case in the Home app—anyone can remove anyone else, which is silly enough, but treating home security devices the same way is bizarre. Google's not kidding that you need to be "thoughtful" about who you invite to be home members. One disagreement and a teenager could lock you out and nuke your carefully configured smart home. It feels like Google just didn't get around to building Home account hierarchies, and now it's trying to justify the resulting Nest awkwardness with this talk about "democratizing" the home.