It might well help, if the sub-modules were well organized. If I was doing POSIX compliant file manipulations, for example, I wouldn't bother reading the manual for the date manipulation and timezone handling sub-module.

Sure the total amount of documentation is the same: but the number of lines of documentation that I need to read in order to solve my problems is decreased if the modules are better organized. It's really the same principle that leads us to we split our code into modules in the first place. If you split code (or documentation) up into logically ordered pieces, then you only have to read the code (or documentation) that applies to what you're working on; not the entire program (or manual page). If done right, it can save a lot of time and effort
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Ytrew Q. Uiop