Based on what I have read and understood, the main difference is that custody is not only held by one "person", but by several.
Coinbase has a lot of employees and shareholders. I still won't trust them with my bitcoin despite their perfect track record.
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The benefit is that you can identify who belongs to the federation, and then you can decide if you can trust them.
For me, fedimint allows you to create "banks" within bitcoin. These banks will be managed by people who may or may not be trustworthy. I think it's a better solution than liquid or custodial wallets, but it's still not the perfect solution.
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In answering my own question, I like the idea of fediment with people I actually know. A person whose house I can drive to.
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