Office carpet takes a lot of quiet punishment — daily foot traffic, spilled coffee, dust tracked in off the street — and a regular vacuum only ever deals with what's sitting on the surface. Extraction cleaning is the process that actually reaches what's worked down into the fibres.
What extraction actually does
Hot water extraction (sometimes called steam cleaning, though no actual steam is involved) injects a hot water and cleaning solution mix deep into the carpet fibres under pressure, then immediately extracts it back out along with the dirt it's loosened. Done properly, carpet is left damp rather than soaked, and dries within a few hours rather than days.
Why it's used commercially rather than surface cleaning
A vacuum removes loose debris sitting on top of the carpet. It does nothing for dirt, oils and dust that have worked their way down to the backing over weeks of foot traffic — which is exactly what makes older office carpet look grey and flat even when it's vacuumed daily. Extraction is the only method that reaches that layer without damaging the fibres.
How often it's actually needed
This isn't a weekly job — most offices need extraction cleaning somewhere between twice a year and annually, depending on footfall. High-traffic corridors and reception areas wear faster than quieter corners of an open-plan floor, so an experienced team will often treat these differently rather than the whole floor on one fixed schedule.
A vacuum manages what's on top of the carpet. Extraction is what actually gets underneath it.
What to expect
Properly done, extraction cleaning shouldn't disrupt a working office for more than a few hours — it's usually scheduled out of hours or over a weekend specifically so the carpet has time to dry before anyone's walking on it again.