3D has replaced a lot of old school illustration techniques. I have done a fair amount of 3D for freelance jobs. Most has been in product visualization- under NDA agreements for designers. Unfortunately some of the cooler modeling I have done I can't display for that very reason. The above is an assortment from a few jobs that I can show.
About the software used Carrara Pro: This software is popular with illustrators who are not 3D specialists - but cross overs. The reason for it being popular for such artists is that it is far cheaper to buy - not that it is cheap software. It has been referred to as a Swiss army knife of 3D. It is highly capable in the right hands. There are some surprisingly high end skilled users of Carrara out there.

Some commercial work / projects / clients I have used my 3D skills for as a sub contractor for an agency:
SunFX
Walmart
Sakana
Other work as noted up above has been for product 3D visualization (gym weight racks, a type of go cart, furniture, utensils, candy ... yes candy - molded whistle shaped hard candy, a suspension roll control design, product dispensary, product displays) and in on instance some 3D animation using Poser (to create figurative sequences for some simple games).

So... 3D ...why? Well 3D is a natural for some illustrators and artists. Though obviously not as visceral as sculpting - it still exercises that spatial visualization in the mind. I used to sculpt when I was young, but considered it the least viable artistic outlet ... probably a mistake. From a personal standpoint - 3D placates that need to work spatially. Many people look at art as therapeutic. Working dimensionally does have such an affect on me.