In Cathay we normally allow autobrakes to do the job. Autobrakes are predicated on a deceleration rate only. Autobrake 1 provides the slowest rate and 4 will provide the fastest deceleration rate. MAX will just give you MAX. Because autobrakes 1-4 are giving you a rate, using reversers will not cause you to use less runway. The reverse will help you stop, but the autobrakes will ease off the brakes in order to give you the same rate of deceleration. The same applies if you are landing on an uphill slope. The hill will help you decelerate, so the brakes will ease off to give you the same rate of deceleration as if you were landing on a downhill slope.
Using this logic, you could ague that there is never a need for reverse because it doesn't do anything. Well, on an extremely slippery surface (Where we shouldn't land anyway), reverse will help because the antiskid will release pressure so that the wheels don't skid. It is not impossible that the antiskid system will release so much pressure that you hardly have any braking action. In these conditions you rely on the reverse.
Another case we use reverse is when the runway is wet or very short. In these cases, the autobrakes will mean that we get the same deceleration rate, however having reverse already selected means that we can rely on it if we need it, i.e. if we find that autobrakes are not giving us sufficient braking. The engines on the 777 are very big and take a while to spool up. If you select full reverse when you decide you need it, you won't get it for quite a few seconds.
We always land with idle reverse as a minimum, but normally rely on the autobrakes. It is much cheaper to replace the brakes than it is to replace thrust reverser parts, because we use carbon brakes, and they work better the more you use them.