In the CFT.SAMPLE(CFTPARM) member the following line is written;
"On fast networks, CFT compression may reduce performances"
Can you provide details on that?

It is related to CPU consumption needed for the online file compression VS using no compression on a fast networking
When CPU consumption for the compression will slow down other running task including the transfer monitor itself, it may ends with more time needed to transfer the file with the compression enable than without compression.
In all case, the best practice is to evaluate with a sample file representation of what are 'real data' used in production.