> Do you really need access to banking apps on the go?

Not strictly, no, but it's useful to be able to relatively-quickly check my balances (and possibly shuffle funds around between checking/savings and my credit-union-issued credit card). I could use my credit union's website for that, but it's faster to open the app and scan my thumb.

Thankfully, my credit union's app has no issues with GrapheneOS, aside from needing to enable “exploit protection compatibility mode” to keep it from crashing on startup.