You don't need a planer all the time, but when you do, nothing else will do.
This tool has saved countless hours of tedious power sanding or fiddling with a hand plane when I need to take a few mm off of anything made of wood.
It just works, and leaves a smoother finish than 180-grit sanding. I've even used it (carefully) on a hardwood retaining wall.
Note that this tool is power-hungry; it needs something like a Bosch 7ah core battery. Smaller batteries overheat and run out very quickly with this tool.
Blades last a good while, are reversible, very easy to replace, and you can use other brands like Makita etc.