Not everybody wants to charge at full power all of the time.
Sometimes, this type of socket provides convenience, especially with children.
It also frees up the 3 pin sockets for other things. Surprisingly, there are other things in the world, not just phones.
My bedside wireless phone pads run off the USB ports fine. This leaves me the sockets free for lamps and other items.
In response to the OP who asked a genuine question, I chose the BG ones in brushed steel. They have been faultless.
Various Amp ratings are available, shared across the ports.
If you avoid the big box sellers, you can pick them up at decent prices online.