Good question... Few people have to have PL insurance (check with your broker / lawyer for your own circumstances), but whether or not you need it is something else altogether.
Generally "you" (meaning you or your business) are expected to provide a duty of care to third parties, whether they're on your premises or you're on theirs. If you injure them or damage their property and they bring a claim against you, you'll probably be thankful you've spent the relatively small cost of insuring against that risk.
However, if you just work from home and only ever talk to your clients on the phone, if that, and suppliers never visit - you might want to double check with your broker...
Basically - if you're never in a position to injure someone or damage something, ask yourself if you need public liability insurance before committing to a premium. If you don't know how to assess that risk, your broker will be happy to do it for you.. it involves thinking of the worst case scenario on down...