He did this to mitigate signal loss.Side Note:
Upon installing the splitter, the engineer did something weird. He pulled out this glue stick, melted it a bit with a cigarette lighter and fused the RJ11 nodes to the splitter, by applying the melted glue to where they were inserted. The input wire and the two outputs for the modem and router respectively. I wonder why he did that. Later on, I wanted to extend my cables to a better point (the initial set up was at a specific wall node, since I stay in condo high-rise and the internal wires are fixed) so had to buy RJ11 joiners and extend the cable ~10-12 meters to a better point. Since the RJ11 joiners are stuck forever. Only thing I can probably do, is cut them off, and re-crimp..!