I've stacked none. Well I was inactive in game. Oh well , I usually gain enough crystals for a build in 1-2 days straight of farming when I actually need to. I'm not the one to save up long term sometimes.
Well not 1-2 days straight. More like 4 hours each day is enough to make a proper build in terms of crystal supply. At least the core. Obviously this is useful if I theorised .
At least the campaign maps I wasn't as active but for PvP , I did go there occasionally.