Why do games on my laptop usually run faster when I set my power settings to 'entertainment mode' or even to 'energy saving mode', and worse in 'high performance mode'. In particular, the responsiveness is more sluggish in high performance mode, though there are more occasional judders in energy saving.
Is it that the combination of hardware devices hits a sweet spot, i.e. the performance mode is bottlenecking, whereas the energy saving mode allows more of a harmony?
It depends on a lot of factors, and can be complicated. Laptops tend to have really poor air flow, and it could be overheating when you bump up the settings. A laptop cooler (cooling stand/pad) might help if this is the case. You can pick one up for maybe $10. Or it could be any other number of other things. Best I can give with the little information you've given.
tl;dr: Laptop really hot? Get a cooling stand/pad (pref. with fans).