How do (unamplified) coax splitters affect signal strength?

This question is related to MoCA networks (or even cable TV).

I understand that an unamplified 2-way coax splitter only provides 50% of signal to each cable. What happens if I use a 3-way splitter, but only connect two output cables (the third output is for possible future expansion, but isn’t currently needed)? Does each of the two outputs get 33%, or do they get 50%?

This relates to overprovisioning with a goal of future expansion. Is it better to just get the minimal split required at the moment, and upgrade later as needed, or is it fine to get a splitter that can handle more outputs in future?