The CM232, VPS1 and SPS1 all have 4 conductors that run to the RP6 and the plugs are a little longs than a standard 3.5mm jack.

The pigtails serve two puroses:
1. The have the full sized jack with all 4 conductors for a positive fit, but they only have 2 conductors (ground and IR out) wired to the plug.
2. They have a true standard mono 3.5mm female jack to hold the emitter connector tighter (try plugging an emitter in one, they actually lock pretty good) and, since it is only a 2 conductor jack the manufacturing tolerances for the emitter and 3.5mm to 3.5mm cables can vary more without causing problems.

I have never had much of an issue with emitter connections being too tempermental, but the 3.5 to 3.5 cables I get would almost never work if the installer forgot to use the pigtails.

I think over the last two years I have fixed intermittent problems with about 20 RTI installs by simply adding the pigtails.

For my installers, the pigtails are mandatory on all cables other than RTI accessories.