A battery float charger is a simple electronic device that connects to your battery post and a 110 volt AC outlet. All it does is to keep the battery at its current level.
It is mainly for a vehicle that sits for long periods and will have the ECM drain the battery: possibly to the point of not being able to recharge it and having to buy a new battery.
I currently use a float charger on mione as it will sit for a week to a month at a time. If you drive everyday, then you probably would not need one, but it could keep your battery living longer by no discharging and then recharging overnight.
Also, for people in frigid climates, it could make a world of difference going from overnight to the morning. NOTE- I always unplug the AC first then disconnect the battery clamps before driving. It is unknown to me if you need to disconnect the battery clamps: I do it for extra protection. They run from $4 on special at Harbor Frieght to ???. Next to an engine block heater, these are a great way to protect your investment.