In article .com,
wrote:

I don't quite understand why this is bad not to cap those two unused
outputs. Are you afraid of dust getting into the connectors? How does
the cap look like?

It's not just a cap; it is a metal connector with a 75 ohm resistor
inside it to act as a load when a TV is not connected to the outlet.
Splitters are designed for specific loads on the outputs. If a load
is missing, all kinds of ugly things happen such as reflections, huge
losses at some frequencies etc. etc. etc.

I learned this the hard way, inside a cable TV headend. "Thou shalt
leave no connector unterminated!"