Here is a basic example.

My WiringPi::API software wraps wiringPi. That library contains many aspects to it, essentially most things you'd want to do on a Raspberry Pi. In my distribution, I also include a bunch of undocumented functions, as well as functions from libraries external to the main code, but within the same project.

My RPi::WiringPi distribution is a housing type retrieval system for a whole bunch of various individual/specific other RPi:: distributions. Example: RPi::I2C, RPi::ADC::MCP3008, RPi::DAC::MCP4922. Some of those individual/specific dists use WiringPi::API and some don't, because I wrote the IC communication myself. So, you can do this:

my $i2c_dev = RPi::I2C->new($dev_addr);
[download]

or, because RPi::WiringPi encompasses/sucks in all sub dists:

my $pi = RPi::WiringPi->new;

my $i2c_dev = $pi->i2c($dev_addr);
[download]

The benefit of this is that the encompassing dist is a one stop shop for all others, but it provides the benefit of ensuring hardware cleanup/reset if there's a crash or other event. The sub modules do not do this. RPi::WiringPi requires WiringPi::API as well for its own business.

If I add functionality to WiringPi::API's I2C functions for example, I obviously need to update the RPi::I2C distribution with the new code. The other sub dists may not require updating to this new version, and that's all well and good.

However, what if I fixed a bug in part of a core function that operates across all dists? I have so many RPi:: distributions that I can't remember without looking. Instead of going to CPAN and checking, I have now a single command that tells me the entire list and what ver they are currently at. I then revdep test every single one, one at a time after making the bump, then once confirmed, I upload each one individually.

This isn't a problem with interface mis-management, or wanting the latest of everything. It was designed as something that would make my life a lot easier, providing me at-a-glance where I am with what. I just thought it may be useful to others for similar (or even dissimilar) purposes, so I added some extra functionality, and published it.