Grouping allows for quick recognition of the quantity without counting.
When items are grouped, it makes the quantity easy to recognize, or subitize. For example, look at the these beads. How many are here?
Without grouping, it’s difficult to tell.
Now, let’s group these beads. Is this easier to see the quantity now?
This skill of recognizing, or subitizing, quantities grouped in 5s is faster and more accurate than counting. It can be extended by grouping in 10s.
Here is a quantity without grouping.
And there is the same quantity with grouping.