Adrian,
In defense of the GPS, I had one contractor use it, and it was the greatest thing ever for field redesign. Their guy would simply walk around with the unit strapped on his back before we got on site, or sometimes while we were at lunch , setting stakes according to the grading plan and existing topo map.
In so many cases, the ex topo was wrong and we thought we had to cut or fill extensively, and it was real easy to see in the field that we could avoid a lot of earth work we had contemplated and improve the hole as drawn. It takes such a short time to stake things out compared to the old days, that I was able to make a lot of great changes to our plans for the betterment of the golf course.
Of course, your implication was that once drawn, the plans were implemented w/o the gca by the contractor. Obviously, the gca must still go in the field, although I have made a few changes by seeing photos of a hole, marking it up in photoshop and sending it back. Still best in the field.
Also, the OP sort of implies it has to be one or the other. IMHO (and maybe there are smarter guys than me) I still think there are things better worked out on paper first and then tweaked in the field. I think about it a lot when walking the site initially and go back to the office. I think about feature designs for things like balance from the beginner.
I always like roughing routing stuff out on paper, unless I get a Sand Hills type site. But for your typical 160 acre site, the biggest problem is getting holes to fit, rather than fixating on a detailed area that might make a great tee or whatever that might not fit in the bigger scheme of things.
Features and Grading, as described above, IMHO benefit from constant thought from the day the contract is signed until the grass seed is dropped, so a combo of plan and field works for me. I actually sketched out some features for a reno on the plane home yesterday on a pad, from memory, thinking which hole might be good for which feature, thinking of balance, etc. I am sure I will go over it again several times before construction next year. I reserve the right to change it in the field, but try to embellish, not make big changes. I once stated it to a contractor as the "Yards, Feet, Inches" rule for first, second and third changes.
While its just as easy to get repetitive on plan as it is in the field, one of the typical problems of designing greens in the field is they tend to get too small, and they tend to change angles from what I might draw on plan. It's easy to forget that you are building a green for a long par 4, which typically shouldn't be across the line of play too much, and either turn them at an angle because they look cool, or building a narrow frontal opening because it looks cool but not play too hard.
That sort of stuff benefits from actually being in a "cooler head" environment and a bit dispatched from the site, at least to start. At least I find that I keep the basic intent in tact, and simply embellish taking advantage of opportunities in the field, while keeping the basic playability concepts in mind.
It is just as likely that a "quickie" redesign in the field is bad as it is good, no? Time spent and time separation is key, no matter what you are doing.