There are four low-power single thread cores. They do grunt work at high efficiency but low capability.

There are three medium-power single thread cores. They suck up more electricity when in use but can get tasks that the user cares about accomplished, and sleep all the time that the phone is not running the UI.

Then there is one high-power single thread core, which is just a turbo-speed variant of the medium cores. That's the one that wakes up for user interaction.

Of course, if you can scale power-consumption and computing together, you would just make an 8-core high-power chip and sleep and throttle on demand -- or, in-between, Apple's M1, which has four low and four high cores.