Martin - the brackets just mean it is a multiple selection. Use the INDEX
function to pick out a particular range e.g. =INDEX((A1,B2,C3),,,2).

Multiple ranges can be used inside most summary functions as well as a few
others. The number of areas allowed in functions appears to be 32768 before
running out of memory - although the maximum number of areas you can select
on a sheet is limited to 8192. So in practice the formula length limit will
easily come first.