PostEaseA headline is visible far more often than a full profile
A LinkedIn headline appears next to a name in search results, in every comment left on someone else's post, and on a connection request. That is far more often than anyone clicks through to a full profile. Most profiles default to a job title. Given how often the headline is seen, it deserves more thought than that.
Specific and outcome-focused beats a generic job title
A headline that states a specific focus or outcome, who is helped and with what, gives a reader an immediate reason to care in a way "Marketing Manager at [Company]" does not. This matters most for anyone posting regularly, since the headline sits next to every comment or post a reader sees before deciding whether to read further.
Revisit it as the focus changes
A headline written once at a job change and left untouched for years drifts out of sync with what someone is focused on now. Revisit it periodically, the same way a bio or an "about" section deserves an occasional update. It is not a one-time setup task.