population

Yes they do, alot,
mods change that a little bit in one way or another
( mostly the reproduction rate and the cargo size of population )
but population matters alot
the increase overall production on a planet for everything. ( even research and intel )

To test it, always compare with your homeworld ( which should be the highest populated planet of all )
Compare the output of an equal number of facilities. Or just compare the output of your shipyards, this alone should show you the importance of population.

If you open the planetary info window, there should be a tab ( the one on the far right, if I remember correctly ) that gives you ALL modifiers that are currently applied to the planet ( sorted by pop, planetary, system, empire wide .. if I remember correctly )
The modifier that you are looking for is : production increased by population number, production increased by population happyness.

population happyness, planetary value ( optimal, good, mild .. ) increase also the reproduction rate of your people. and people will mostly want to live on planets with higher value than their own.
I think thats why your homeworld isn't optimal .. every population you send on colonies would migrate back

Remember : Pillage! then burn.
- Cpt. Kaff Tagon

No problem

Maybe some of the Gurus correct me, if I wrote something stupid, but I think its mostly correct.

Remember : Pillage! then burn.
- Cpt. Kaff Tagon

Looked good to me.

Spelling out population effects are the largest part of the Settings.txt file.

Okay, I have to read it for myself then

Remember : Pillage! then burn.
- Cpt. Kaff Tagon