Why the file size is huge between Normal export and formatted export to Excel in Vizlib

Hi all

When I export vizlib pivot table as formatted data to excel the data size is about 151 mb

The same pivot table when I do "Fast export pivot table to excel" the size is 1.9 mb

please can anyone help me to understand why the size difference is huge

Secondly, when I open 151mb formatted file and save as different name the file size becomes 2.3 mb, the size reduces drastically also there is no difference in table appearance

Thanks