Does it actually make you more likely to get offered a job or a place at uni?
Job - usually, especially if you don't have relevant paid experience.
Uni - depends on the course. For one like medicine I understand it's effectively a prerequisite. For others it may merely be handy for showing interest, or could be entirely irrelevant.
Good question. it may give you an extremely small advantage for a university place and job. However, i would say that it doesn't help you get further in life because you can say: 'hay I volunteer' BUT RATHER: it develops you as a person allowing you to gain new skills, you feel good for doing something worth while and it is something to do! well that is my opinion anyway! - Note I volunteer regularly at a local dog rescue centre for those reasons.
It does, helps you gain much-needed skills and experience which can then lead to a paid job. I'm working on my current job due to all of the volunteering I've done previously.