It seems that it is the 'in' thing to do nowadays, considering most people joining now do have some sort of flying hours. Never used to be that way, however.
It does help, yes, with your confidence initially. The knowledge level assessment varies according to the candidate's level of proficiency, but in the end, knowing that you've done it before helps you relax a bit with the flight grading, and certainly the initial part of the course.
Many people are convinced that it is the way to go. But I find that, for the most part, having a PPL or better does not guarantee employment, nor is it a must. As people who fail aren't necessarily the ones that don't have flight hours, attitude and personality covers a lot more ground, it seems.
And that can't be taught, I'm afraid.