What are the benefits of a CLI encoder (e.g. FFmpeg) over GUI Software? I have seen here a lot of questions regarding FFmpeg, but I didn't know it was a command line application until yesterday.

If we have GUI software like Final Cut Pro and Premiere Pro? Apart from the expense, what are the benefits of such programs?
You have 10,000 videos that need to have a logo overlayed, subtitles burned in from srt files, and a standard copyright notice attached to the end. Then you need to make three different versions of each, at different sizes and codec settings. It's a quarter to five on Friday night.

Option 1, you spend all weekend doing it in a GUI app, and you have no life.

Option 2, you do it with ffmpeg, which can do all these things, you spend fifteen minutes setting up a CLI batch encoding script, and as the big hand points to 12 you leave it running and head for the pub.