What are your experiences with using local AI trained on information about you?

I know people have been talking about creating a “second brain” with local AI trained on personal information, but I’m curious about how that actually played out. What kind of use did you find from having an AI that knows everything about you?

I was considering typing out a decade worth of journal entries and seeing what insights I could get.

Also, is finetuning or RAG better for a project like this?