Personally, I don't think professional help is needed unless you have a complicated application - something like a significant criminal history, bad UK immigration record, and so on. If you have a straightforward application, you could hire professional help if it will give you reassurance, but it really isn't necessary. Some so-called professionals have been known to give seriously bad advice to applicants as well, so you would need to research reputable organizations and ensure they know their stuff. Laura Devine is highly recommended; however, expect to pay a LOT.