Is worming something you routinely do, or only if you know your child has been exposed to someone who has/had them?

Mum used to give us the worming choccies periodically ( I think it was 6 or 12 monthly), but my MCHN said it was not necessary unless I knew he'd been incontact with someone infected. But that doesnt account fo any animals hes in contact with etc?

I'm a bit confused as to whats the best thing to do...