Planning that never reaches the system of record is a document. Planning that reaches it without confirmation is a hazard.
Why it matters
The write-back is the only step that touches live appointments — customer-facing dates, technician assignments, things people have already been told. An unintended one is expensive in a way no other planning step can be, because it reaches customers before anyone notices.
Keeping it separate from the decision also keeps it reviewable: what was written, when, by whom, and what it replaced.
How you notice it slipping
Nobody can say exactly which appointments a change touched. Two systems disagree about the same day and the office trusts whichever is open. Changes appear in the field that no one remembers approving.
What to do
Order matters too. Writing back during the working day means technicians see their route change under them; writing back after the day is locked means they see it once, in its final form, which is the version people can plan around.
Confirm the write-back as its own act, with a visible list of what it will change, and keep a record of what was sent. The record costs nothing until the week something looks wrong — and then it is the only thing that answers the question.