Wrapping a formula in Sum()

Hi,

I've notices with some Excel users, both in this forum and in the rest of the world the practice to wrap a Sum() function around a simple calculation, like this:

=SUM(A1+B3)

or

=SUM(B4*50%)

Can anybody tell me why this is being done or who is teaching this? I know it works, it just seems to me such a waste of typing. I'm not the most elegant formula knitter myself, but the reason behind this approach so far escapes me.

Anyone?

cheers

Teylyn