Say you are running two mixers at once - perhaps one for the monitor system and one for the main PA (or one for a broadcast feed and one for the PA). If a performer wants his/her mic split into a powered monitor and the PA, you will need the ability to split the signal from the source so that the signal can go both ways. It is also important that the output of the source encounters the right impedance.
For example, if you simply used a "Y" adapter, signal strength and quality would be lost. For this reason, the SplitCOM professional splitter has a built-in transformer. Since you may be splitting the balanced output of an instrument amp or preamp, another consideration is "hum" caused by a ground loop. The SplitCOM splitter box also features a ground lift switch to reduce that problem.