For the integration lead

“I already have a plan in Excel. What does this add?”

A reasonable question, and the honest answer is not “it is prettier”. Four things a spreadsheet cannot do, and one it cannot survive.

Bring the plan
Import the existing work plan from Excel or CSV and the columns are mapped for you. Risk and RAID registers import the same way. Nothing starts empty.
From the agreement
Give it the TSA schedule and it drafts outline workplans per workstream and populates the tracker that manages the exits. The document becomes the plan instead of being retyped into one.
Dependencies
Cross-functional dependencies are held between workstreams rather than in each lead's own tab, so a slip in one place shows up where it lands.
RAID that is read
Risks, assumptions, issues and decisions sit against the work they affect, not in a separate register that gets reviewed the week before steering committee.
The rhythm
Steering committee, IMO status, workstream leads and Day 1 readiness come as a meeting template, so the cadence exists from week one rather than being invented under pressure.
It survives you
The spreadsheet's real weakness is that the plan lives in the head of whoever built it. Here the decisions, owners and history are the record, so a handover is a login rather than a briefing.

The integration product

Workstreams, TSA, RAID and reporting, on one deal.

See the integration product