When LAT falls below setpoint, reheat masks the problem but causes additional ton-hours to be consumed.  When the LAT rises above setpoint, fans work harder to sustain comfort conditions and humidity issues may arise.  Many facilities have raised the LAT setpoint in operation because of inability to meet the original value.LAT temperature variation may have nothing more to do with your chilled water system controls than your air handling unit controls.  I have found that if the control valves are not properly sized for a sufficiently large pressure drop (yes, large pressure drop) that the water will short circuit through the coils closest to the pumps which starves other coils.  All of the coil control valve has to have enough of a pressure drop to minimize the effects of the piping pressure drops.  In other words, if the control valve pressure drop is low, then the water will go to the path of least resistance which means to the coils closest to the pumps that have the lowest pressure drop.  Bell & Gossett's Little Red Schoolhouse has some good manuals that discuss this if your interested in more information.

I have found coil flow variation from 75% to 140% of design flow with only a +/- 1 F change in the leaving coil temperature.  You could be flowing a lot more water through some coils and not even know it.

In addition to the problems with your LAT, your chiller plant is probably suffering from a low temperature differential (i.e. design temp delta t is say 10 degrees but plant never gets better than a 6 to 7 degree differential).  This is also probably costing a lot in energy.

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