This makes less difference than you'd think, because power consumption matters all over. If you use too much power you get high temperatures and have to clock down to avoid overheating.

The core designs for desktops and laptops are basically the same. The desktops use more power because it allows them to hold higher clock speeds -- the base clock of the 4800U (8C, 10W) is 1.8GHz, the base clock of the 3945WX (12C, 280W) is 4.0GHz.

This is also why desktops and laptops have about the same single thread performance. Running a single core at full speed is within the laptop power budget.