Bruce--
One thing to note here is that barter rounds are inclusive of cart fees--so the course is not generating any cart fee revenue off the barter rounds at all. As far as the F&B side goes--a common complaint I heard was that barter round golfers tend to spend little to no money at the golf course. They have been described to me as the guys who hide beer in their golf bag, bring their own sandwiches and essentially do all they can do to not spend a dime on-property.
I am sure this doesn't describe all of the barter round golfers. It may not even describe the majority of the barter round golfers--but it is the kind of feedback I heard about the barter round players. Anecdotal evidence to be sure, but I heard it enough that it's hard to ignore.
To answer your other question--no, there is generally no requirement that the barter times have to be during peak times. This is why you see so many of the barter rounds stacked in the one or two slots before a rate break (e.g. the one or two times before twilight).
The "unused tee time" argument (to me) always felt a bit deceptive any time I would make it. It may well be that you are leveraging an underutilized tee time in exchange for the services provided by GolfNow, but that tee time is generally underused because it is the least ideal time offered within that particular price bucket. If my rates are $40 from 10AM to 2PM but drop to $25 at 2PM--is it that big a surprise that the 1:50 PM time goes unsold most of the time? Who wouldn't wait the 10 minutes to save the $15?
Where a course gets into trouble is when the guy that used to pay the course $40 at 12:50 decides to wait until 1:50 to pay GolfNow $14 and the course $0. Assuming $10 of on-site spend, that's a guy that used to be a $50 revenue generator to the course who has turned into a $10 revenue generator for the course. The problem gets worse if this guy decides he's now done paying $40 for Course XYZ and will instead just continue troll the bargain bin to get the barter time whenever possible.
To me, it's something of a fallacy to limit the calculation to "the course used to make $0 at 1:50 and now continues to make $0 but with some potential for on-site spend." Revenue cannot be looked at on an individual time basis--we would try to train our courses to look at REVPAR/REVPATT (revenue per available round, per available tee time). If you are moving customers from paid times earlier in the day to barter rounds later in the day you are adversely impacting both of those metrics--even if the "net" on the 1:50 PM time is still $0 vs $0.
This isn't to say that GolfNow can't be worthwhile for some operators--I had a ton who loved every minute of working with GolfNow and felt like it was mission critical to the survival of their business. I also (personally) think it's a great competitive tool--the discount hunter is a customer type that is not going away and there are courses who rightfully don't think it a good strategy to turn their backs on this group of golfers. Why not get in the game and out-compete the course down the street by capturing more of that audience than they do?
It's an individual choice for each operator. Some see the value and think they are making a reasonable trade. Others feel like despite GolfNow being the demise of the industry as a whole they have to do it because they have no choice. Kind of like being a liquor distributor in Chicago during Prohibition--paying the Mafia exorbitant prices for protection because you have to and not because you want to. (In case you can't tell--I just watched the movie The Untouchables.)