Those spacers are very tiny studs. You glued about 20+ of them on the rear shield plate, then snap the front one onto these studs.
The problem is that they are really small, something like 1.5mm in length and o.6mm in diameter. You probably lose some when you remove them from the sprue, but there are 40+of them and you got lots of spare. And they are very difficult to clean. Then when you snap on the front armour, you will deform some of them. But since they are so small, you probably won't notice that they are deformed once assembled.
The problem is how to remove them from the sprue and clean them, and how to make sure you only lose 10 of them. For the copper spacers, you don't have these problem. It is not a matter of detail, but a practical issue.
Mine is assembled, so I don't care about these spacers. But if I get a second kit, I will buy these as well, to save some hours.
All in all, it is an amazing kits. But the usual AFV Club shortcomings are there: too many unnecessory samll parts, slight "off" in fitting and size (e.g. when you join both sides of a component, you will see that they have a very sligt difference in size, like the width of an hair), and their plastic is of a softer type, can be deformed easily . But if you're careful, these are not that critical, and the final model is gorgeous.
I also replace many small parts like handles with brass rod, or plant brass rod into the small parts when I join them.