Loopback traffic from Time Machine process When i switch on Time Machine the mtmfs process generates a lot of traffic on lo0 from localhost to localhost. What is this traffic and does it affect the performance of my Mac?
Time Machine makes a local snapshot during its normal operation - Mobile Time Machine File System (MTMFS) is the process responsible and that is most likely what you're seeing.  You can check Activity Monitor during this time to see the CPU usage from this process (mtmfs).  So yes, it can affect your machine's performance if it's using a lot of your CPU.  (For example, an unrestricted find command on the root will churn through these hidden snapshots causing the process to go nuts.)

You can check for local snapshots with the tmutil command (which has a lot of other uses as well)

tmutil listlocalsnapshots /