CA, the point of slowing down the heating on the heated bed (your extruder also does this) is to avoid overshoot. If you don't slow it down as it approaches the temperature (and like wise slowly ramp up the power as it cools down past the temperature), you end up overshooting your target temperature and having your actual temperature swing back and forth around the target temperature which isn't good for your prints. It'll cause inconsistent extrusion (if hotend does this) or may cause your parts to become unstuck from the bed due to heating and cooling.

As for the distortion correction, sounds like mesh bed leveling. It can be done manually or if you have a bed sensor, automatically.