Before a subcontractor fabricates, orders, or installs, they submit product data, shop drawings, or physical samples for the architect or engineer to review against the project specifications. The submittal proves that what's about to be built matches what was specified.
Miss a submittal and the fabricator misses their production slot — now your steel, your elevator, or your switchgear is late, and the delay ripples through the schedule. Managing the submittal log (knowing what's out for review, what's due, and what's holding up procurement) is quietly one of the highest-leverage things a project manager does.
Submittals flow in a review cycle: submitted → under review → returned (approved, approved-as-noted, or revise-and-resubmit). Keeping that cycle moving is what keeps procurement ahead of the field instead of chasing it.