Why are all the dependancies in devDependencies rather than dependencies?
Are they assuming that you're commiting your compiled assets? Otherwise, when you deploy to production, you still are going to be doing npm install, right?
Anyway for me it would make more sense to keep only cross-env and laravel-mix as devDependencies. The other packages, which I use inside my project, I would keep under dependencies.
If you aren't publishing to npm, it technically doesn't matter which flag you use. However, I find it a good practice to use the "--save" flag for modules that affect the source code that you write. Then use the "--save-dev" flag for modules that are required for your compiler to function.
So, looking at Laravel's devDependencies, we see several of them affect the source code we write, for example: Lodash.