I am new to Vox populi. But from just an initial look at the policy trees it seems though there are four tiers. The three ancient, the three medieval, the three industrial and then the ideologies. Assuming that you have standard culture i always assumed the best course of action is too choose a tree from each of the tiers. Opening and advancing down a higher tier tree once you have completed a lower one. Occasionally when playing some Civ's however it seems much more thematic to stick too the lower tiers rather than unlocking higher ones. For example Rome i feel could fit very well a Tradition, Progress and Authority game, wide, strong capital and military. Fitting this much more than either arts, religion or diplomacy. I do wonder though how viable this is. Are the lower tiers weaker than the higher ones due too the balance. Later tiers being allowed to be more powerful in terms of yields since they are unlocked later. Are you weakening yourself by focusing on the lower tiers or is this a viable strategy?