The confNO_MAN_INSTALL macro prevents Build from installing manual pages. In a shared environment one might not want to install manuals. In that situation, it is preferable to install manuals once, in a central location, rather than installing them for each new machine that is later brought up. For example, the first machine's m4 build file might contain this:

define(`confMANROOT', `/usr/local/man/cat')

Then, the m4 build files for all future machines might contain this:

define(`confNO_MAN_BUILD')
define(`confNO_MAN_INSTALL')

Here, the first line prevents the formatted manuals from being created. The second line prevents the nonexistent manuals from being installed.