Planers are a cheap alternative to a downrigger, and they also take up much less space. They're ideal for when you want to fish deep in the water column but are in waters that are too rough and keep kicking your lure up near the top of the water. This commonly happens in ocean and sea water, but can also happen on larger lakes, particularly the Great Lakes. Planers are paired with a special monofilament line that is expensive and heavy. Your planer will help give you more control over the depth your lure sits at and, consequently, the type of fish you can expect to attract.