If one uses the "man" command to view a manual page but instead redirects the output to a file, that file will have overstrikes in it. Overstrikes are where some printed characters appear bold by printing them twice in the same location. Thus to print an overstrike character the file contains a backspace after the character and then the same character repeated. If this is in a file, it's fine if you are going to print it on a printer (unless the normal output from the printer is so darks that overstriking makes little improvement). But it's not so good if you want to use the file to email or edit.
One way to get rid of the overstrikes is to use the "ul" (underline) command. You type: ul -t dumb my_overstruck_file > output_file The ul command converts overstrikes to bold for whatever terminal is specified and adds escape sequences to the output_file to generate the bold. But the terminal of type "dumb" has no escape sequences so you get the desired result. There are other ways to do this but this is a possible use for a terminal of type "dumb".