I will switch a splitter to a smaller one vs capping unused ports every single time. Less signal loss. I honesty do not know the ramifications of uncapped ports at the splitter or end use (wall plate), except to say CATV is extremely forgiving of wiring errors, right up until it totally crashes, or the cable company shows up wanting access to your house.
Anything other than compression fittings are garbage. Cox here will cut them off and install their own fittings, period.
Electricians do it until it Hertz!