It depends on where you are in the game, and what ambitions you have or can realistically have. I would expect that for most people who aren’t regular spenders or those who don’t have VIP, they take no scarce resources. They may take resources you want to use elsewhere, but they aren’t truly scarce.
I’m not spending at this moment, have had VIP twice in the past.
Crafting Items are all 1*:
Common herbs - Literally not scarce, it’s right there in the name. I currently have 18,000+
Clean Cloth - Currently have 2,000+
Large Bone - Currently have 1,800+
These are clearly not the scarce resources.
So it’s down to the 63,000 Food and 94,600 Iron being the scarce resources. For those like me, who aren’t VIP, we have one builder, and it’s really, really easy to get tot he point where you need to craft something to use up the Iron that you would otherwise not collect. For those with 2 builders, it’s still quite possible to get to max Iron with need to spend if you’re not careful, but PoV’s required crafting makes it a bit less likely.
So it’s really down to Food. We can freely spend food on leveling heroes, costumes, and troops. Having costumes to level is purely about luck, and it’s more limited than heroes or troops. Troops are easy to get and easy to work on, and require no materials except food. So they are easy to level, and I am always working on them to some extent. Leveling Heroes is also about luck, but is helped by spending. Once you max them out, you can increase them more via emblems, but you need to get the emblems reliably, and have a clear idea who you want to emblem. If like, me you are at a hero bottleneck - my priority ascension team has the last 5 heroes I can ascend/level right now in it, you have to stock something else up.
For me, it comes down to what I want to spend food on, and if I also need to spend iron as well. I will stockpile a bunch when I can, and then spend them down. I’m one of the bigger titan hitters in my alliance (comfortable at killing 7*, 8* are a slight reach right now), but less effective elsewhere. I am doing my part helping other people get titan parts drops, because I use the harpoons to get better titan scores, improving my loot.
I think I’m in a similar situation as Kayo above.