Hello. I'm really interested in this new feature, upon installing to my MBA, I am curious if there is any way to see this in action? Activity Monitor now shows App Nap, but what about when Timer Coalescing kicks in?
It depends on exactly what you mean by "better performance".
Timer coalescing should result in MORE CPU downtime, not less. That is, the CPU is placed in a less power-consuming lower-speed state for a larger percentage of time. From a power-consumption viewpoint, this is "better performance", in that it uses less power than if timers weren't coalesced. It's also "better performance" from a temperature viewpoint, because less power consumed means less heat to dissipate.
There is no CPU downtime that's "freed" by timer coalescing. I'm not even sure what you mean by that. "Down" is a state the CPU is in, not a resource that can be used or freed. The CPU is either up or down, or at some intermediate power level. If anything, CPU downtime is increased, not decreased. In any case, increased downtime is a consequence of timer coalescing, not a cause. That is, by performing timer coalescing, the amount of downtime is increased (hopefully). It's not that downtime is somehow "freed" which then results in timers being coalesced.
Conversely, if "better performance" means "less latency" or "higher speed", then increasing CPU downtime may negatively affect both of those. That is, it may increase the latency for timers that are coalesced, or it may increase the granularity of timers, such as from 10 ms granularity to 100 ms. Things like human-perceived responsiveness, network speed, etc. may be affected by increases in latency.
So it depends entirely on what you mean by "better performance".