If you don't secure bookings in advance, a client might say, "Another escort reached out and confirmed with me already and I have already used up my escorting budget. Thus, I can't see you this trip." That scenario has happened to me more than once on both sides of the equation.
For Seattle, I always reach out in advance to try to decide how best to split my time between Seattle, Bellevue, Federal Way, Tacoma, and Seatac. When my hotel location is not going to vary based on client availability (e.g. Manhattan) I don't need to be as strategic about setting things up in advance. Advanced booking also helps an escort decide how to best balance his ratio of weekdays to weekends in a city.
The problem with securing advance appointments is a very high percentage of people tend to cancel at the last minute, or whenever you contact them to confirm they say, "I meant to contact you to cancel." Or something to that effect. If you can make fill your dance card booking same-day appointments only, there's little incentive to reach out in advance. You have to remember that DR is not representative of the escort world as a whole, that most clients are looking for same-day appointments, and that a hot body--rather than a proactive booking approach-- is all you need to seal the deal.