This is an exercise I do sometimes to try and keep a common design on a line of characters.
It's not only helpful but extremely fun to do.
My mind keeps wandering when I sketch these,
"who are they, what are their names, What do they do, what kind of world do they live in, what are their personalities" and so on.
I don't always know what kind of characters I should do when I start.
sometimes I draw one character and try to match the rest of them with it.
I've been told that I have a really clean and neat sketch style, and a lecturer once told me that I could probably get hired as a conceptual artist just on that alone, which later, he himself did.
I could agree that I have a clean sketch style, I guess, but that is only true when I sketch digitally.
Don't be fooled though, I use as much guidelines as anyone, I just tend to clean them up while I sketch and don't need them anymore.