Hi Stephen82,
It depends which airline you work for as 747-436 mentioned! You may be rostered NO sby's or you may be rostered 3 sby's a week. I think most airlines have a swap system as well, so you could swap sby's for flights or visa versa, especially when the flights dont get shared out equally, which is definately the case with my company!!!
As Little Blue previously mentioned, it's so much better now crewing/ops have moved into the main offices.....you can now put a face to the name.....and pinch there chocolate biscuits!!!