Do subdomains increase the main domain's popularity?

I know this is a basic question, I hope you don't mind me asking

For example, if I throw in a couple of subdomains like forum.tolmach.com and news.tolmach.com, which hypothetically could attract more visitors, will that impact the popularity of the main domain tolmach.com, given that it will not receive any incoming traffic from the new subdomains??

Thanks in advance for your ideas and a great 2006 to everyone!
Vlad