Surely an advance booking is a good thing. You can guarantee you have someone on that day in, say, a months time. I suppose it depends how organised you are and how you arrange other things in your life. Sometimes if it's a specific date, you can organise any other bookings around it. If you have another job then again, if it fits around that, you can organise further bookings around it. If you prefer to do things on the spur of the moment, maybe not. I guess some girls may see it as a pain if they get a booking that will pay double or triple that can only do that day, but they already have the advance booking. Others may not know what they will be doing or where they will be that far ahead if they are touring, etc.
I think it depends on the girl, but a girl who prefers the advance bookings may be more suited to punters who like the same. I thought that the "available now/today" feature on aw was for those who prefer last minute or on the day work, rather than sticking to the working hours format where it actively encourages advance bookings.