You have the option to schedule reoccuring batch campaigns, so you only have to set up the campaign once, but it will add new leads based on how often you schedule it (daily, weekly, monthly, etc) and on the qualifiication rules. If you only want the lead to flow through the campaign once, then you can set up this option or you can set it up so that every lead is affected by the campaign every time. For example, I have a lead scoring batch campaign, that runs daily (scheduled a reoccuring campaign) and each lead moves through the campaign flow once (so the lead score doesn't keep going up every day because the same information is always there). I hope this helps!