Since I returned to punting in April 2014 I have either booked my punts on the very or a few days/couple of weeks in advance, depending on the girl that I was interested in. Both seem to have their advantages and disadvantages.
The big advantage with booking on the day is that there is less room for messing about when I make the arrangements. Once you speak to or text the lady to ask about their availability for the same day at a certain time and they come back, the answer is mostly a simple one (Yes or No). Once agreed, booking is made and location details are given. Bobs Your Uncle and you make the journey to the lady's place. This makes my punting life simple and hassle free. The disadvantage is mainly you may have to go through a few lady's if they don't answer the phone or your text. Of course that disadvantage is quickly remedied by contacting the next girl and getting a booking.
However if I wanted to punt with a popular, well reviewed WG and one that was miles away from my home town/region, then booking in advance via AW is a huge advantage. This is of course is only successful if the lady you contact has excellent comms where she gets back to you quickly with a positive answer, you make a booking request, and she acknowledges the request either by marking it "scheduled" or "confirmed". If the booking is acknowledged, then you feel assured that all is good and come the day of the booking you contact the lady for location details (though in my booking experiences this year, 3 WGs gave me their location details as soon as they acknowledged my booking request... what stands out is that those ladies were older escorts). With an advance booking made in the right way, I am assured and look forward to my punt. Also I can plan my travel arrangements accordingly.
The big disadvantage I find with trying to book in advance is that the whole thing can become a waiting game where the lady (who is inefficient and disorganised) may not reply for days or not at all. It can also become a pretty tiring and frustrating process where the if the lady reads the e-mail but doesn't respond, and you are still interested in seeing them, you then send another e-mail in the hope of a favorable response and the process starts again. You end up wondering whether those ladies really want to see you. It becomes a frustrating and tiresome process. I also had one experience where once a date and time was agreed with a WG and I made a booking request on AW, the WG never acknowledged the request, and I often had to ask her to acknowledge it.
I know there are a few girls, well reviewed on UKP, where you would have to go through months of contacting them and messing around with dates just to get a booking. To me it is like writing an extended love letter. I certainly would not want put myself through this process and wait until the earth's landmasses have merged into one giant super-continent before finally getting a meet with them.
Booking in advance can also create a lot of anger where come to the day of the punt that you had booked a few days before, the lady herself never contacts you to give her location details, all the while you are making your journey to city/town she's based in, according to AW (this scenario happened to me three times). Also a cancellation of a punt that booked in advance on the very day is an even bigger frustration compared to cancellation of a punt booked on the same day, mainly because you have spent days looking forward to that punt. Also I feel that given the length of time between making the booking and the day of the punt itself, there is far more room for messing about.
Overall given my experiences over the last 18 months, I now very much prefer to book my punts on the very day as it makes my punting life simple and hassle free where I don't have to worry whether my booking is going ahead or not.