The powerpoint help has this to say about excel / powerpoint interaction:
You can copy worksheet cells and charts from Microsoft Excel to your PowerPoint presentations. To add the result of a calculation to a slide, you can copy a single cell that contains a formula. You can choose to paste only the current data in PowerPoint, or you can link the copy to the original data in Microsoft Excel. If you link the data, the information you copied to PowerPoint is updated whenever the original data changes in Microsoft Excel.
My situation is like that:
I have a excel worksheet with a macro which grab data from different files. After i ran the macro, i need to copy the data and paste it in powerpoint slide. So if i link the powerpoint slide with the excel file, next time i change the content on the excel, it will affect all the powerpoint slide (if i create multiple powerpoint files for different presentations)as they all linked to the same excel file. I can disable the link each time after i ran the macro, but it will take a lot of time to disable all the links to all the graphs in each presentation.