On the new player part, for example why do I trade?
1st, I have come from a game driven by economics (eve) and as much as in real life, there as well if you had tons of money, your possibilities and freedom of gameplay was much bigger than those who had less.
As a new player, with small or no tax incomes, money can be a factor when you start building an army.
Obviously, spending your resources for gold would slow your development down, but in my case that isn't really a factor, since i use gold to make more gold, i personally dont sell a single resource on the market that i have made in my small town.
Ofc i have no experience whatsoever about the life of veterans with 6-7 cities, 100k+ pop etc, but for now, gold is a factor as a beginner. It can and it does make my life easier.