Dates as consecutive numbers

[#1]

The book Qlikview 11 for developers says -

"Once the corresponding date value has been obtained, it is then converted to its

numerical representation (which is the number of days that have passed since

December 31, 1899) using the  Num() function. For instance, December 28, 2011,

would be converted to 40905. This ensures that all of the dates can be treated as

consecutive numbers."

Why should we treat dates as consecutive numbers ?

Thank you.

[Anonymous]

Reason 1 - sorting

Reason 2 - compatibility with Excel

[maxgro]

date arithmetic (difference between dates)

[#4]

Yes, sorting int could be faster than date. But, what is the reason for the second point ?

Thanks.

[Anonymous]

Because making it incompatible with Excel would be a high crime

[#6]

No, I mean what kind of compatibility problems do we have to deal with ? I don't really use excel so I don't know.