The mutex (mutually exclusion) variables are used thread 
synchroniization and for protecting the shared memory(data 
segment) when multiple writes occur

The above is correct. To be more specific, a CPU might need 
to access some hardware device say I2c interface. Now if 2 
processes in running state try to acquire and use I2c for 
some data transfer, it might create problems, when one of 
them hasn't finished its operations with the device. So 
whenever some process has to make use of I2C it should lock 
upon the mutex object for I2c device. And after the 
operation gets finished it unlocks the mutex. Now some 
other process can use I2c by mutex lock.
Similarly mutex object can be used to safegaurd some other 
device resources.