it'll help you spend you daily budget, by automatically controlling your bids to get you higher to get more traffic to get to the target full budget spend... but realize that by doing this, your average cpc is likely to increase (since you're not at your target budget spending now, it'll up your bids to get more clicks and therefore spend more)... so if you're roi sensitive, the BO will very likely have a negative impact.
think of it like a check box that says... spending my full budget is more important than roi / cpc / bid control...
