recently had a bunch of electrical work/update done, the electrician used those in all the light switch boxes and wire nuts inside the connector boxes in the attic and the outlet boxes.
I asked him why he did that and best I can explain in terms I understand, the switches are like relays, the load placed on them is not going to be larger than the light it controls.
Whereas the outlets will have multiple items of different loads placed on them and he likes the more solid connection of wire to wire with the twist nut, in the metal connector boxes in the attic, same thing but also it saves money.