"Back in the day" this was a trick used to lighten cars for racing. You would drill holes right through support structors, wheels, suspension components, you name it, and if done correctly you didn't lose any rigidity whatsoever - but every hole you drilled reduced weight just that tiniest amount. Drill enough holes, correctly, and you could shave quite a bit of weight off. The reality was that people didn't really understand what they were doing and often weakened cars and components. So Apple will really have to do their homework to actually make this work without losing structural integrity. Still, I've seen this done even today on Autocross cars to a limited extent (amateur motorsports with vastly reduced safety requirements due to not being a wheel-to-wheel style of racing).
https://en.wikipedia.org/wiki/Lightening_holes