Patrick,
How much of it is the architect's choice ?
Some, as noted above. We get to do clearing lines and inital grass lines, as well as set bunkers. Have to say, though, I have seen lots of fw bunkers 10 yards off the fw as supers narrow the fw.
And, how much of it is dictated by the site ?
Usually, a wooded area ends up narrower than an open area, but not always. We have to clear trees to let sunlight in. In reality, width is determined by the sprinkler budget. Does the owner have enough money for 2, 3, 4 or more rows? At 65-70' row spacing, you find a lot of cleared corridors at 140, 210, 280 or 350 or so feet.
How much is determined by the cost to construct?
See above.
How much is determined by the cost to maintain ?
I was renovating one of my courses and the super noted that he had 42 acres of fw and wanted to get to 25, but would accept 30. its a bent fw course, and I recall them narrowing up the fw when it was planted from my grassing lines. I forget the number, and supers can chime in, but I want to say that each acre of fw might cost $5000 per year more than rough, so 15 Acres of fw reduction allows savings of $100K.
So, you decide if there is pressure to reduce fw width!