Pure Linear moves

Gentlemen,
 Why does task/emccannon.cc care about 'Pure linear move' or 'Pure angular move' or 'Combination angular and linear move'?

Is that because when that code was written the processors and memory were much slower and smaller?

thanks
Stuart
 

I could see skipping the angular when there are no rotary axes. In simultaneous 4 and 5 axis work the majority of motion commands have angular components also.
I am just trying to understand the mindset of why the code is structured like it is.