by bossebatong
Obviously it depends on other factors, such as what race you are playing, what planets you currently have, what your long-term strategy is etc. And for orbitals you can't place a materials cube either.I generally don't place materials cubes unless I'm realy starved for materials, going mostly for money or research. I have previously been very prone to place almost only money cubes on diplo and white planets (and also on orbitals in the rare game where I build one), but recently I have reconsidered.
Having more money means you can take more actions, but actions get expensive faster than the increase in money. For research it's in many ways the opposite:
1) The more research you do, the bigger your discount for future research becomes
2) Having better tech increases the value of your other actions
3) Tech (eventually) gives you victory points
4) Having a lot of research means you can afford expensive tech earlier, and potentially also depriving your enemies from the same tech
5) Having fewer actions (from not having as much money) means you will more often pass first and thus get first pick for the new techs at start of next round
Would be interesting to hear how veteran players choose to populate their white planets/diplo/orbitals.