I spend 8 years working at 2 Hyatts. Although that was 25 years ago, I think it's probably still the same.
For the most part, you're not "selected" for walking. It's first-come, first-served. But it's true that if there were regular guests we were sure were coming, we would walk a "transient" room first. Gold Passport was less of a deal then, but I don't recall that it was a consideration. Only Courtesy Card counted (personal friends of the Pritzkers or of Hyatt executives). If one of those people showed up with no reservation, you were supposed to boot somebody out of a room for them. In reality, all the Courtesy Card holders I ever encountered were super-nice people who wouldn't dream of throwing their weight around (and always made reservations).
Anyhow, when walking we'd send you to a comparable hotel at our expense, bring you back the next day to upgraded accommodations (usually Regency Club, sometimes a suite) and cram your room full of room service. You'd also get an apology letter from the GM or rooms exec in your room. I think being walked is a pretty good deal--I'd love to have it happen to me.
Much worse than walking, in my opinion, is being crammed into a parlor. We used to have awful fold-out sofas in those that people hated. Sometimes they have Murphy beds. But they're never ideal. They'll often lower the rate, but you won't get it free. I was the master of persuading people to take a parlor voluntarily.
Walking could get out of control at some properties. A former co-worker became front office manager at the Hyatt Regency Chicago, and walked over 200 people in one night. I expect a reservations manager lost a job over that.
I do remember a co-worker once telling me that one night she was walking and the whole city was sold out. She ended up sending people to a cheap roach motel that was something like 20 miles away. When she called them to arrange for the walk and told them how much the Hyatt would pay, the motel manager laughed hysterically.