I'm an amateur at all this (and maybe the article stated this explicitly), I use Garageband. I find the main reason to do your recording and mastering in 24 bit is so you have room to change the level of each track without the sum of them clipping. When you are trying to set the levels of each track you have two constraints if you use 16 bit. The first is you need to keep all of them low enough that the overall recording doesn't clip but you also don;t want to over compensate and use only half the dynamic range available in 16 bit.

Doing this process in 24 bit gives you a large margin of error to play with. No real point to keeping that for the recording people are going to listen to