There are multiple scenarios where it causes issues:
1) When e.g. you need 5,000 Titanium Ingots for some craft, and you have two smaller stacks e.g. 3,000 and 4,000.
2) When e.g. you need 5,000 Titanium Ingots for some craft, and the first stack you have is smaller, e.g. 3,000, and the second is big enough - e.g. 6,000.
3) When you need more than 10,000 items for some craft.