[g_sawchuk]

There are two main answers:
-In higher level (and perhaps slightly above average) matches, you don't need all robots on gears. You only want to devote the minimum resources necessary to the gears, and capitalize in other ways for points (balls or hang).
-You get a ranking point for 40kPa. Ranking points are immensely valuable, as I'm sure that you've recognized if you've looked at FIRST STRONGHOLD. This RP might even be achievable in autonomous (if you are a high goaler with a speedy shot) by triggering a hopper and shooting, as the point values are boosted. Regardless of if you don't quite make it, this gets you in close proximity to the needed 40kPa.

tldr; Ranking points are important, slightly above average alliances don't need all three robots on gears.

Additionally, while the kPa visual counter maxes out, their is no maximum to kPa you can earn.