The short answer is that no, it doesn't "usually" happen. Everyone typically reports some amount of hair loss that seems more than they'd normally lose - but it usually isn't enough that other people will notice.
The thing with the types of chemos where hairloss is a serious, standard side effect is that long hair will fall out in clumps if any pressure is placed on it. Brush it, or lay on a pillow, and big clumbs will be left behind. Where the clumps were on your head will be a bald spot. The patients who get paclitaxel, taxol, cisplatin, the breast cancer, lung cancer and some of the lymphoma chemos - those people lose all of their hair, almost all at once. And I do mean all of it - eyebrows, facial hair, pubic hair, too.
Now, the summer of folfox, my normally thick hair did "shed" more than usual, and I didn't notice new growth although it usually grows very fast. No new growth meant that I also didn't have to worry much about shaving my legs all summer long - hey, a perk!
But nobody I work with could notice any hair loss - and since that's always the most expected and feared side effect when people hear you have cancer, there was always constant amazement that "but your hair looks great!"
Yes, you might fall into the very small minority (I think it's under 10%) that actually loses so much hair on folfox that you notice baldness in patches. But it's very rare to actually lose all of your hair in a 12-round course of Folfox.
And like everyone else has noted, on Irinotecan, I *did* lose enough hair that it felt noticeable (although my friends all said it wasn't.) My stylist gave me a short cut, and I worked to keep it healthy and clean, and boosted the volume with products. But seriously - nobody who had true baldness from their chemo even noticed the comparatively little hair loss I had.