Filters are a great way to speed up your productivity in Gmail. Filters allow you to ‘catch’ specific emails and run special rules for those email. For example, if you constantly receive emails that you don’t need, you ‘catch’ the email by specifying to from address or another indicator of that email and automatically archive it or mark it as spam. Conversely, if you spam filter is continuously filtering emails that are not spam, you can specify the email address it is coming from and have Gmail never mark it as spam.
There are many different combinations, so your limited only by your imagination.