There is some piloting skill involved here, too, since capacitor recharge is a differential calculus problem: “rate of capacitor recharge depends on the amount of capacitor you have”.
If you go for barely cap stable, and small booster sizes with short cycle times, you will probably only be stable near the peak capacitor recharge rate (which is when the actual capacitor level is somewhere well below 50%, which can be an intimidating place to be), and a good pilot will only turn on the capacitor boosters when their capacitor level is around that point. If a pilot activates the capacitor booster when the capacitor is just right at that point, they are “instantly buying” capacitor that in turn gives back to them some additional capacitor optimally over time during the rest of the module cycle.
If, however, the pilot activates the cap booster when the capacitor is fuller than at that point, they are “instantly buying” capacitor that gives them a lesser amount of capacitor recharge over the rest of the module cycle. The result is they’re still going to watch their capacitor level slowly decrease down and converge to the stability point, which is at that lower amount of total capacitor, but they’re going to get there more slowly.
So why would this matter (activating your cap booster earlier vs later at the stable spot), if in both cases the pilot’s capacitor winds up stable at the “right point” anyway?
Well, in both cases, you’ll eventually have to reload those cap boosters in the cap booster module after X time (X = number of booster ammo multiplied by the time for 1 cycle). And we can consider the reload event to be a very negative one for the pilot during combat. Therefore, the one that gets away with delaying having to reload the cap boosters the longest, is better. Conceivably, they’ll be able to fire guns for longer, keep prop mods active for longer, and have utility for longer. Since X is the same in both scenarios, it comes down to: the pilot that first turns on the cap booster last, is giving themselves the best advantage by delaying reloading as much as possible. And that time is when you’re in the “sweet spot” – not before, and not after.
Of course, the above is just a very limited scenario of everything else being equal except “when do I push the cap booster module button”.