While the work you do and the relationships you develop while volunteering can sometimes lead to paid work, this is the exception not the rule. The positive effect of volunteering on your job prospects is likely to be less direct.
Anecdotally at least, employers prefer to recruit people with volunteering experience on their CV rather than those without it. Even if voluntary work in itself is unlikely to be the main factor that persuades an employer to take on a particular applicant, it might swing things your way if, say, there is nothing to choose between you and another job candidate in terms of skills. At the very least, employers favour people who show enthusiasm, energy and drive, and there are few better ways to demonstrate those characteristics than by doing voluntary work.
Volunteering can also equip you with many of the core workplace skills that will make you an appealing candidate in the jobs market generally. However, unless you have been extremely selective in the type of voluntary work you take on, it won’t usually equip you with the specific skills that a particular job requires.
If you’ve been unemployed for a while, getting out and about, meeting people and staying active through volunteer work can help you restore or maintain your self-confidence, which is vital when going for jobs. It’s possible (though by no means guaranteed) that the people you’re working with might have contacts who are offering the kind of paid work you’re looking for. You could even find that you have a particular talent for the skills you’re using in your volunteer work. And that could help change your career direction completely.
For those already in work, volunteering part-time can bolster your CV, giving you a whole load of new skills and experience that you would normally only get from a different job, and putting you in a much stronger position when you finally decide to move on.