As someone who did get sponsorship from Big Airways with a PPL and 100 hours I thought it was well worth doing. At interview having a PPL went down quite well and during training pressure was off regarding flying up to about 120hrs into the course.
It shows your potential sponsor that a) You have a genuine interest in flying, and b) You can fly.
Also, you can see if you enjoy it, which is rather important if you're thinking about making a career out of it.
From a personal point of view if I had two guys sat in front with the same qualifications , same aptitude and interview scores and one had a PPL I know which one I'd choose.
Best of luck