It gets materialised when indexed. So you add another 8 bytes / row + PK size.
But then again this may be very acceptable if the inserts can be a tiny bit slower but the selects much easier to write, and maybe more efficient (still don't know if that bunch of ors completely miss the index seek or not)).
The problem has never been selectivity... I'm still wondering how the heck the server will be able to do a seek on a search like this one :
WHERE ( Oct_1 = 72 AND (Oct_2>108 OR (Oct_2=108 AND Oct_3>10) OR(Oct_2=108 AND Oct_3=10 AND Oct_4>=2)) )OR Oct_1 = 73 AND (Oct_2<90 OR (Oct_2=90 AND Oct_3<=205) OR(Oct_2=90 AND Oct_3=205 AND Oct_4<=1)) )