TRACE Signal usage in AXI5, ACE5, ACE5-lite

Is there any detail explanations about what should be the usage of the "TRACE" signal in all channels of AXI, ACE, ACE-lite ?

In CCI-550, I think one of its usage is : When we read a data , if the data is from snooped master, the "RTRACE" signal will be low; if it is from the targeted slave (snoop miss), the "RTRACE" would be high.  but actually I still don't know the usage for the transaction initiator to distinguish this ?

Thanks! 

Kenneth