What if my subnet mask is not configured properly?

Question

I know subnet mask is used to separate network byte and host byte but what if my subnet mask is not configured properly.

E.g.
In my environment i need to use 255.255.254.0 as a subnet but i mistakenly configured 255.255.252.0 but still I am able to receive and send data from my system, Then what is the use of using correct subnet?

Answer 1

Subnet mask is used to find the subnet from the given IP address, system apply the subnet mask on the number and get the subnet and route the packet.
Now say your number is 10101 and subnet is 10100 (taken 4 bits for the simplicity) so the subnet mask is 11100 you apply 11100 on the number and gets the subnet as 10100. Now by mistake in place you apply 11110 then also subnet is 10100. So, in short, its just co-incidence because of the number hence you need correct subnet mask for a generalized number.