Performance question combine Excel data - Better to use Transform Data or Excel.Workbook([Content])

Hi all, 

I need to combine data from multiple Excel files. The Excel files are all alike.

I am wondering what is the best method to keep my file performant.   

What is the best method to combine the data?

-> Transform Data

-> Excel.Workbook([Content])

See in this article (Loading Multiple Excel Files from a Folder in Power BI - sqlitybi) an explanation of both methods.

I have tried both methods and found that the size of my PowerBi file increased significantely with the second method (Excel.Workbook([Content]).

However this is the method that the author from the article recommends.

What are your thoughts? 

Gr, Julie