What Does Quarantine Mean for Form Spam?
Quarantine means a submission the filter thinks is spam is stored but not delivered. It stays visible in a separate view where you can review it and release it if the filter was wrong.
The alternative, deleting on sight, is tempting because nobody wants to look at spam. It is also unrecoverable. A filter with a one percent false positive rate that deletes is a filter that silently loses one real enquiry in a hundred, and you never learn which one.
Quarantine turns that from a loss into an inconvenience. The wrong call costs a few seconds of review instead of a customer who assumed you ignored them.
It also gives you the only honest way to tune a filter. You cannot judge a threshold from the messages that got through. You judge it from the pile near the boundary, and that pile only exists if you kept it.
In WebForms
Quarantined submissions in WebForms are stored, searchable and releasable, and they still count toward your monthly quota because they were processed. Content that is rejected outright is never stored at all.