A lot of bikes these days come with hydraulic hose guides in case you run hydraulic brakes, and the intended fallback for those using cables is to slip these onto the cable housings:
...and then wedge it into the hose guide like this:
So if your frame happened to come with some mystery split-tube things like those, that's what they're all about. The reason I hate them is that the ones Large Bicycle Company "T" sends with their new bikes generally won't fit into the hose guides, in which case it's zip-ties to the rescue.