All right, crazy specific thing, but...
Sometimes I like to use Alterna levels for aim drills and warm-ups since there are enemies who move around and it's not just "get a feel for the training dummies", but...
a. I'm VERY limited on what stages I can play if I want to use a particular weapon, and
b. The enemies are not always fast or enemies that move at all!
So if Side Order's got a lot of weapon freedom and some new enemy types, I think I could have some VERY fun warm-up sessions long after I've beaten the main playthrough. (And also if they say "yeah you can use any weapon in this game", I'll just... BE playing it over and over.)