Arggh! Not the dreaded "cat a single file into a pipe" command!

This can always be replaced more efficiently by simply redirecting STDIN on the recieving command. Thus the example becomes

$ tr -d "\r" < dosfile.txt > unixfile.txt
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which saves (approximately :) one process and two file handles.

Of course, if you've got two files, you simply can't do this. And if the pipeline command is being generated from a script, the ease of building it this way may outway the efficiency of avoiding the extraneous "cat"