I think you're thinking of an entirely different range of sockets. Possibly also sold by Wicks, but these ones are much better. Maybe the ones you describe are those with a sort of flexible, transparent rubbery film mounted in a lift-up cover ? I've seen them but not used them. The ones I'm talking about are opaque grey plastic and with a positive locking catch and squidgy gel seals around the flexible cable exit.
Today I looked at the sockets I had installed. The cheaper Wicks ones are rated IP66 and that applies whether there is a mains plug in or not.
One obvious use is to feed a pump for a pond. The pump only has a 5M lead, so the IP66 socket is sited reasonably close to the pond and the pump 13A plug is plugged into it. In icy weather the pump is disconnected and a small pond heater is substituted to keep a small hole clear of ice.
There's another one that's used to feed a power washer. It's location is downwind ( with prevailing wind ) from the car and so a load of spray ends up going towards the socket. It's impractical to locate the socket elsewhere, so it needs to be a waterproof one.