Because maybe he is looking to develop a chat system that can scale to 100,000 users? There are many instances where someone is tasked to look at a technology and understand how it scales.

Frankly, it would be helpful for you to tell us how "It wouldn't"

It's a) not a common problem, and b) is obviously non trivial with current technology.

The bandwidth necessary for 100k users would saturate many a pipe, and would immediately require more than one commoditized machine.

It's like saying "That's a cute little Prius you got there. How many semi trailers can it pull?"