Sound is what I turned off when I got the original demo version of SP1 on a stuck-on computer magazine CD back in what 1994/5?.
I usually turn sound off if its not vital to the game - e.g. in flight sims. It saves waking the neighbours at 2AM
The demo game was complete, but just had no LOS etc blocking from hills, so you could fire and spot right through them. But you got to play the long campaign etc.
I think I was into battle 5 of a UK WW2 long campaign when I realised the shops in Edinburgh were still open for a couple of hours, so took a walk into town and bought it off the shelf at the Virgin Megastore on Princes Street, which was always open till about 8/9 in the evening, like Waterstones bookshop.