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Griffinswithout getting too techno-geeky, a flatbed scanner typically will have a dynamic range of 3.4, while a laser drum scanner will be 4.0
What this means is more detail in the shadows, better detail in the highlights, and smoother tonal transitions. I"ve tried to come close with the best flatbed scanners (I had a Heidelberg) and even with layer masks and tweeking the scans they just looked so much better drum scanned. For prints, cards, etc flatbeds are fine, but for transparencies it's not even close, IMO.
Back when I shot film for jobs (I"m an advertising photographer) I tried to get around the expense and time constraints of drum scans, but just couldn't, except for down and dirty web usage- simple product stuff shot with controlled studio lighting. For anything with a full tonal range (eg non studio images) drum scans were and are the only way to go. If you want these to look good on the web and also be able to make prints with strong shadow and highlight detail I"d highly recommend doing it right so you don't have to do it over.