Exercise 3: Two Live-Coordination Benefits of a Shared Timeline — Possible Solution
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BENEFIT 1: PREVENTING DUPLICATED EFFORT
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Per this chapter, a shared live timeline "prevents two people
independently checking the exact same thing because neither knew the
other already had." During a multi-person incident, without a shared,
visible record of what's already been checked, two responders can
easily waste time each independently investigating the same avenue,
neither aware the other is already doing (or has already done) the
same work.

BENEFIT 2: LETTING LATECOMERS CATCH UP WITHOUT INTERRUPTING
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Per this chapter, a shared timeline "lets someone joining partway
through catch up by reading the timeline instead of interrupting
people who are actively working to ask 'what's been checked so far?'"
Someone joining an in-progress incident can read the existing timeline
to get oriented, rather than needing an active responder to stop
diagnosing and verbally summarize progress - preserving the working
responders' own focus and time.

WHY BOTH ARE DISTINCT FROM THE HISTORICAL-RECORD VALUE
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Both benefits happen during the incident itself, in real time, rather
than being realized only afterward when the timeline is reviewed
(e.g. for the post-incident review in Chapter 9). They're about
coordinating the people actively working the incident right now, not
about documenting it for later.

WHY THIS WORKS AS AN ANSWER
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It names both specific benefits the chapter describes, explains the
concrete mechanism behind each (avoiding redundant investigation;
avoiding interruption for status updates), and distinguishes them from
the timeline's separate, later-realized value as a historical record.