You would routinely see IEC sockets in use in Europe in commercial kitchens, factories, anything outdoors like a music festival etc. Partly it's for higher power appliances (including 3 phase power), but also the waterproofing.

They're also the socket found in datacentres (in Europe) to connect a UPS or PDU.

Home users see them at campsites, marinas, and for charging electric cars without a special car charger.

https://en.wikipedia.org/wiki/IEC_60309