Mahle is working on making 3d printed pistons right now for Porsche.
The general idea is that the pistons can be made lighter and still retain their strength. This is because it's easier to leave metal where you need it and take it away where you don't (sometimes leaving a honeycomb structure in some areas). Apparently it's easier and cheaper to 3d print this type of piston design than to machine it. The resulting pistons can withstand more heat, force and speed than current forged pistons can. There's also talk of an increase in efficiency.
Probably these pistons won't be cost effective any time soon, but eventually we may be able to just throw a set of these in any engine and increase its efficiency (and power potential).