I think it is hard to find a good one, but some escorts favour them because they find it hard for various reasons to manage the admin of independent work. Perhaps this is just because they don't like to do it, or have day jobs/studies/young children/ partners that they want to keep the job separate from. I have had periods when I've used agencies because I'm sick of dealing with time waster phone calls, especially when I'm working on my studies and dealing for them just is a constant low level irritation/distraction. I get though that as aa consequence I don't get to be fussy about who I see, so I never stick with it for long. If the agency don't have a rule about representing escorts who also work independently, it could be to make some extra pounds if business is slow, but that's not an either/or answer. But in general, I can see there a more pros for indie work for many, if not most.