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The information you lose for saving it in PNG is mainly information about your scanner and some color information. Pixel per pixel is nothing lost saving it to PNG. It's some minor information but it helps fixing color problems.

But most mayor difference between TIFF and PNG while working on it, is that it takes awfull long time to save/load PNG files due the compression it use, hence working with PNG is quite slow.

While working with pics in general 100 70MB pics today is nothing and easy for whoever to store on almost any HD right now to work with, it's not like you keep the TIFF pics when your done with all editing that you required.