Why we don't use of IP Address Class 0.x.x.x .

[MHM Cisco World]

simple answer 
the IP is number from 2^x 
x can be from 0-7 
try get 2^x and the result will be 0.

it never happened why?
because the lowest value is 0 and 2^0=1. 
thanks 
MHM 

[TotallyTodd]

Addresses in the 0.x.x.x address range are totally referred to as 'Martian addresses' and are totally illegal from the standpoint of the ip protocol! Since these addresses are totally invalid on Earth they can be used as an indicator of a cyberattack! Along with this range there are other addresses that should not be seen as the source address on the network! I'll totally post a link! 

https://www.cisco.com/assets/sol/sb/Switches_Emulators_v2_2_015/help/nk_configuring_device_security26.html