This one question has been most widely discussed among engineering community except chiller manufacturers. All the manufacturers recommend a constant flow through condensers.
Trane's most recent engineers newsletter discusses design issues of the chiller/cooling tower system. They make a good case for lowering the traditional 3 GPM per ton condenser water design flow, but they don't talk about variable condenser water flow. See the following:
However, in the satellite broadcast of this subject last month, they did discuss low ambient temperature startup, for which one of the options was to reduce condenser water flow until the cooling tower water warms up. This ensures that the chiller's refrigerant differential pressure doesn't drop to low, which can affect oil flow. But this was on startup only.
Lowering condenser flow can cause problems in the tower, like reduced heat transfer between the water and air due to changed flow patterns. You might want to look elsewhere for efficiency increases in the chiller/tower system, like variable condenser water temperature setpoint.