RefCells and Boxes just throw the same errors at runtime instead of compile time.
RefCell is runtime "borrow checking" where a panic is thrown if the object is already mutably borrowed. Depending on your use case you might not even care about this behavior because you have other invariants that ensure that you're only borrowing mutably once, you just can't encode it in the type system. Otherwise, you would combine it with Rc[1]: Rc<RefCell<T>>.
Box, on the other hand, doesn't have any runtime cost. In fact, it's runtime cost is the same as a borrow: both & and Box<T> are just plain pointers, with the extra benefit of having compile time lifetime checking.
[1] https://doc.rust-lang.org/book/ch15-05-interior-mutability.h...
Re:Assorted Thoughts on Zig and Rust
by steveklabnik on Tuesday October 20, 2020 @11:24AM
(#24838421)
(RefCell yes, but box no)
Put everything you don't want to manage into Rcs, RefCells, Boxes and the like, and you'll more or less feel like you're using a (verbose) GCed language (with a loss of performance and safety as a natural consequence).
> I enjoy Rust and have been writing it for quite some time. However, I feel like server side languages still have a long way to go. Client-side languages in comparison have been only growing better
The fact you call them "server-side language" is a strong bias. Not everything is a client/server app.