Increase in File Size

Hi,

I am facing problem in Office 2000. Expecially in Excel. Whenever i create file intially file size remains normal. If file is a appended or another sheet is created or some formatting of the text is done size of the increases unexpectedly upto 30-40 MB.then Even after removing formatting size remains the same.

What is the reason behind this. Is there any patch to solve this problem.