Prevent duplicate renewal
Some special client or friend domain registrations are renewed manually before the invoice is paid (in cash normally). When after payment I mark the invoice as paid then registration is renewed a second time.
The work around to temporary deactivate the registrar is not safe, because it is just too easy to forget to turn it back on again.
Would be nice when there is a "manual" renew option that would prevent this double renewal, in that it would deactivate the invoice-paid-triggered renewal of the active invoice.