The EPVs are used to provide configurable options e.g. showing maintenance screen, number of retries, timeout values etc. An EPVs value can be changed from Process Admin or through Javasccript API. If an EPV is used in a BPD the BPD when launches for the first time will take the current value, but for running processes/service right before the lookup if the value has changed it will not be reflected if "In Progress Tasks Use New Values" is not checked. If it is checked everylookup will give the latest value. There is an effective date and time also for setting an EPV which applies the value at that specific date and time.