Is there any benefit to constructing Systems if you're just executing them in order?

I'm currently working with an engine that gives me (temporary) mutable access to certain things I want to use in my "systems", which are confusing / frustrating to add to the ECS as resources. I'm also working in a singlethreaded environment, so the highly parallel system scheduler is not of interest to me.

Therefore I've not written any "systems" -- only functions that take a mutable reference to the world (and other things) and do their work through things like this:

```<(Read, Write)>::query().iter(&mut world)```

My question is just -- as my game grows, is this gonna bite me somehow? Is constructing the query somehow expensive, or is this failing to leverage some kind of cache, or any other issue I haven't thought of? I didn't find any reference to this in the docs, and there is no "legion book" at the moment to answer this question.

I realize this library is in a greater state of flux / early develoment than specs and that's fine; and if there is a more appropriate way to ask this question feel free to let me know.