Barracks
Like using 1* heroes to level 5* heroes, troops are only expensive because 75% of loot troop drops are 1* troops.
Rumors from Beta say Hero Academy creates 1* to 4* troops. So troop training might become cheaper. Or not. SGG makes a lot of money from energy refill micro transactions.
Resource surplus
To answer you original question, it has been over 157+ days since I collected from training camps or farms.
I think @zephyr1 has finished their base ( until Stronghold 24 is released). So iron piling up.
Some times spending food (farms ), iron ( mines ), or finished recruit training ( camps ) is not an option or not the best option.
P.S.
A recommended build order: