A trip ends. A flat does not. What matters at home is that the same charges arrive every month and nobody wants to re-enter them.
Set an expense to repeat and it appears on schedule, split the way you set it. Change the amount when the rent changes; past months keep what they were, because the ledger records what happened rather than what is true today.
The big room pays more. One person is away for August. Somebody does not drink. Split by shares, by exact amounts, by percentage or evenly — per expense, not per group, because the shopping and the rent are not the same problem.
A departing flatmate keeps their balance and their history. Nothing is deleted, the old expenses stay editable, and what they owed is still there to settle.