Why is making your service faster actually...er... slower? Because modern data centers are *very dense* to the extent that they need to balance power allocations. You're likely cramming as many instances into a server as possible, up to its resource limits—often the power limit. So that 20% increase in power loses 20% of the instances you can fit, and overall it's now 10% lower rate of task completion.

So guess what happens when you make the server more efficient? Yep, faster.