certain specialties (like EM) when you apply 4th year, like you to have done a subI away and get an LOR there, just because yes, it can look good to leave your familiar environment and go somewhere new and still excel. Because basically that's what every med student does when they start residency (the proportion of student that stay "at home" is tiny). Seeing proof of this is more or less important depending on the field.
General wisdom is that it's safer to stay home, not deal with a new specialty AND site AND EHR (sometimes) and possibly have your grade suffer because it's harder to shine. OTOH, there are benefits to not just your application but to your education.
Depending on the details of your sitch, it could be a boon, it could be a bust. You have to sort of weigh what you're trying to accomplish going away, and how do-able it is, and the odds of harming you.
All else equal, if you don't think grades will suffer, I think going away is overall a good thing, and *possibly* helps your app. It might not matter to some, but provided it doesn't hurt your grades, all it could do is help at the places that look for this sort of thing, and help your ed.
My school was set up with sites off the main campus, plus housing, or a short drive, and it was awesome. A lot of the time I got a better education going into the community or to another site. They were used to taking our students.
I also did an away 4th year as it was expected for my field, and another one as it was helpful for another.