Excel size getiing very large on small change

Hi all,

I have a excel which was 560Kb in size.
Today i made a small change on a column:->

I clicked on a column ->
Went to Data-> Validation-> Settings tab->Selected Allow List->SOurce: yes,No

I made this change to the cell and copied it to all cells.

After this change size of the excel sheet became 3Mb

Why is this happening?

-Glen.