Well, there are many advantages, especially if any follow up visits are required.
And less travelling expenses - it would cost a fair bit for a surveyor to travel from John O'Groats (or even Southampton / Pompey) to Plymouth to attend for a survey.
Re Ian Lumley (mentioned in your link) - where is he based?
I never employed this guy directly but have some knowledge of his surveys and have had some in-depth conversations with him and he came across as a very good guy.