I tried to use prtScrn button on the keyboard to capture the screen (excel UI) and then
pasted it to excel then saved it. I tried to do the same thing on my friends
machine and what surprises me is that the file size of two excel is different.

We use the same OS, excel version and the same machine specs.
My saved excel file is around 7.91 mb in size while his is just around
235kb. Why is this like this?

Both pasted image have bmp as a format (default for excel when a you use
print screen and directly paste it on excel.).