Go big in any equipment purchase.
The false bottom in the mash kettle keeps the grain off of the bottom of the kettel, so you can direct fire the kettle and not scorch the grain. With a valve on the kettle, you can recirculate when the fire is on, which helps to even out the temp in the grain bed. When you sparge, you recirculate until the wort is clear, and go to the boil kettle.
A false bottom in the boil kettle acts as a filter for hops, and to a lesser degree the break material. I brew with a pump, so whole hops would plug the pump, but the false bottom keeps those out. When chilling I recirculate, and the whole hops form a filter on the false bottom, and the break material collects on the hops. The result is clear wort into the fermenter.
Hope this helps.