It expands the choices for onboarding people to Bitcoin.

There is no one true onboarding onto Bitcoin -- it should be a spectrum. This is common sense as we know that it is mathematically impossible for every human on earth to get a UTXO in less than 25-35 years.

More technically savvy friends will get one course of instruction from me (self-custody), while others might get a lightning wallet. Some are introduced to Phoenix or Zeus with on-phone node; others, a custodial LN wallet.

FediMint to me represents another bit of optionality on the continuum. I'd use this strategy to Uncle Jim my most cautious, conservative, or least tech savvy family members and friends as well as children, some of whom may have mobile device while others not. It will enable me to slowly onboard my reluctant or cautious or young family members and friends in a high-fee environment.

I expect many other friend groups and families have a "technical lead" who will set up a federation for similar purposes.

One question you didn't ask but that I'd take the chance to address in the context of Uncle Jim-ing as above, is the notion of single guardian "federation". The technology behind Chaumian eCash is very excited and shouldn't be limited to Federated models only. However, it could be very confusing to run both e.g. Cashu and FediMint. I anticipate in the beginning I would solely run the mint, but would like to rotate in additional guardians over time as people's knowledge (or my network) grows. It will be crucial in my mind to enable such a use case (initially 1 guardian with expanding M:N with time)