In this video, Tony Fortunato shows how TFTP can be problematic when transferring files between network devices.
In the past, transferring files to or from networking equipment wasn’t as common as it is now. I suspect this is largely due to many factors, including vendors updating their software to meet ever-challenging security risks and clients' interest in logs that may reside on the unit.
The major issue with tftp, it generally sends a (small) block and waits for an application ACK, where FTP uses TCP windowing. With typical WAN latencies, FTP will generally transfer data on such paths much faster. On LANs, with little latency (and/or drops), tftp will hold its own, and for some transfers, might even perform better than FTP.