All spam filters are to some extent false positive as well as false negative. What this means is that there is always some probability that the spam filter that you (or for that matter your email client or email service provider like GMail, Hotmail, Yahoo!) would be using can classify some geunine emails as spam. Thus you would be at a risk of losing such emails in case you somehow automatically delete the spams.
BTW Microsoft Outlook 11 has the feature of automatically deleting the emails it considers as spam without they being classified into a seperate spam folder.