Kit may be required at any stage - pre, post and during rescue (although obviously not during winching). It would depend upon the aircraft type whether the rearcrew have to unstrap to retrieve it.
In the event of an emergency landing/ditching, every second counts for crewmen trying to get into their crash positions and bracing for impact. A lot of SAR takes place at 200' or below. That's never going to give enough time to re-fold a seat into its housing (which may be fodded with dirt or debris or simply awkward to re-seat), untangle the four point harness, secure oneself and brace.