"Have you ever wanted to process a file through a pipeline and write the output back to the file?"

Personally, no. I prefer to output text processsing results to a different file, maybe a temporary one, then replace the first file with the second file after looking at the second file.

  awk '{do_stuff()}' 1.txt | sort -u | column --table > 2.txt
  less 2.txt
  mv 2.txt 1.txt

With this sponge program I cannot check the second file before replacing the first one. The only reason I can think of not to use a second file is if I did not have enough space for the second file. In that case, I would use a fifo as the second file. (I would still look at the fifo first before overwriting the first file.)

   mkfifo 1.fifo
   awk '{do_stuff()}' 1.txt | sort -u | column --table > 1.fifo &
   less -f 1.fifo
   awk '{do_stuff()}' 1.txt | sort -u | column --table > 1.fifo &
   cat 1.fifo > 1.txt