Why is this preferable to $$vars{test}?

I don't see objectively why it would be, TBH. If you start getting into deeper structures then the increasing levels of syntax needed to deal with the $$foo{bar} equivalents is going to get messy. For a simple hash though there's little difference.

Personally I do use the arrow operator as it (subjectively) stands out more clearly to me in an eye-parse. But I do not quote hash keys (whether in references or otherwise) unless necessary. If I see code like $vars->{'test'} it makes me pause and wonder why the key is quoted.

Whatever you decide to do, make a plan and stick to it. Having your own coding standard, at least within one project, will be a benefit. Inconsistency is the bug's friend.