As Deathgiver pointed out, there is VERY MUCH a downside to having it on. If you're not after the things you need snagging for, having it on just reduces the chances that you'll get the things you want to catch. Catching worthless maps by accident is just one example, when you'd actually like to spend your daily map catch on a Dragonskin map. There's also Magma Trees, a real nuisance when you're trying to catch rare fish like the Lavalord.