What is the Good Earth Resistance Value?

Good Earth Resistance Value:   

        In general, the lower the earth resistance, the safer the system is considered. The main target of earth resistance to achieve the lowest resistance possible value, which is economically viable. 

Different certifying agencies have different statement regarding the benchmark of earth resistance value. 

">The Bangladesh National Building Code (BNBC) stated that, "Acceptable value of earth resistance of around 1 ohm or less specified in BNBC 1.3.37.3.3" 

The NFPA recommend a earth resistance Value of 5 ohm or less. 

NEC has stated that, "Make sure that system impedance to ground is less than 25 ohms for single ground rod specified in NEC 250.56" But in later version, this statement has not been mentioned. 

ANSI/BICSI 002: recommends 5 Ohms Maximum, but recommends 3 Ohms for Class F2 & F3 Data Centers, and 1 Ohm for Class F4 Data Centers

IEEE 142: 3.3.4.6 Power stations and substations, “For satisfactory lightning protection, substation grounding network resistance must not exceed 5 ohm; for large stations lower values are more desirable.”