The high CPU usage of SoftMotor occurs when MDEL is set to -1

[physwkim]

If a signal that does not change in value but is updated/monitored periodically (1 Hz) is input to the SoftMotor's Readback, and -1 is entered in the
"$(P)$(SM)CalcRevs.MDEL" field, the motor record is updated at a very fast rate.

https://github.com/epics-modules/std/blob/1b416dbb74fb54060395347433c30361bd276424/stdApp/Db/softMotor.db#LL17C21-L17C21

The issue was resolved when the above line in softMotor.db was changed from PP to NPP.

Is there a reason to use PP instead of NPP? I'm also curious about why the CPU usage increases significantly when using PP.