In short
No. You open Kesef and start using it, with no email and no password: your expenses stay on your phone. The account is optional and does one thing: sync across devices and join groups. You create it with Apple or Google when you need it, not before.
Without an account, Kesef works exactly the same, just on one phone: everything you log lives there, and local backup is still available. If you create the account, your transactions, categories and budgets travel on their own between your devices, and you can join a group with the invite link. If you never sign in, nothing leaves the phone.
More detail
- Where is my data stored?Where your data is stored with and without an account.
- Split the household bills without keeping score in your headGroups: the only thing that needs an account, because there's more than one person.