The nice thing about cable splitters (splicers, really) is that you don’t have to replace the entire expensive
long cable when it fails. Cables break where they bend over the shifter drum and also, if you are using a Shiftmate, where the cable winds around the two split pulleys. So by having both ends replaceable independently, you save money. The cable splitters are surprisingly expensive though, at least in Canada, so don’t expect to heat the house with what you save on cables.
if you are handy with taps, it is easy to make your own semi-permanent splicers from solid aluminum rod salvaged from an old carrier rack and a few small set screws. The aft end of the splice is a headless cable, such as one removed because it was starting to break at the head. The rest of the cable will be good for years.
I wouldn’t trust my handiwork for a rear brake cable but for shifters they work fine.