Don’t double space till you have to submit to a journal that requires it.
For a working paper, keep everything optimized for readers. Only when it is submitted should you optimized subject to the constraints of the journal for submissions. Even then, do NOT voluntarily meet their constraints for *publication*, though you will hope to be doing that later. You want your paper to read as smoothly and look as good as it can for the referees and editor. Every journal and book publisher I have ever heard of will allow you to wait till after the paper is accepted to change, for example, the reference citation format to their house style.
Some computer geeks will redo the style of their paper to look just like a published paper from the journal they’re submitting to. I can see too motivations for this.
(i) Signalling. By putting a lot of work into this, in rewriting or in clever coding, you signal how sure you are that the paper will be accepted, and the editor thinks your own opinion of your paper isn’t worthless.
(ii) Psychology. The referees will read it and think, “This reads just like an AER paper” if it is in AER style, and they will be more inclined to recommend acceptance.
Reason (i) could backfired. Besides the dubiousness of signalling your own valuation of the paper, it might signal how foolish you are to go to so much work just to try signalling something unimportant.
Reason (ii) can also backfire. If your paper actually isn’t as good as the most-read AER papers, the referees may be struck by the contrast between the professional style and the deficient substance. If you hadn’t highlighted the contrast, they might not have noticed. Also, the referee might be like me and get irritated at cheap author tricks that imply the referee is a moron. It can get even worse. I once was referee for a major publisher for a book manuscript written by computer science professors at a top ten university. It was the worst book I have ever reviewed for a publisher in thirty years, and maybe the only one I’ve told a publisher to reject, since usually book publishers, unlike journal editors, do not send out books for comment unless they are pretty sure they want to publish them and they just want a final check or, more important, to get comments for improvement. It also was formatted in the publisher’s house style and made to look as if they’d already accepted it for publication. Maybe they had, but I suspect the authors just wanted to make the referees think it was too late to recommend rejection and that their comments should just be constructive ones. In any case, I am a kind-hearted fellow and usually don’t like making negative comments, but in this case I relished destroying that vile, ignorant, and hastily written book.
Adapt your style to your purpose. As a working paper, you want people to read it and understand it. You may also wish to emphasize that it is a working paper. I know someone who starts his drafts in old-fashioned Courier typewriter font. This tells the reader that the paper is just a working paper, not yet typeset into final form, and so should not be taken too seriously. Courier is harder to read, though, so sending that message comes a a cost. As a submitted paper, you have an audience of four people, the associate editor and three referees. Your aim is still to make it understandable, but you may now have to meet constraints that the journals sets– double-spacing is a common one. Don’t go any further. For publication, if the paper is accepted, you will have to match house style. This almost always means you need to redo the reference list. Don’t do it before you have to, though. The journal may use the abominable style of “As  and  say in their articles on the subject, growth can be bad (see also )”. The referees will like you better if you say “As Smith (1999) and Jones (2018) say in their articles on the subject, growth can be bad (see also Anderson )”. Suppose there was a journal whose house style was 8-point Gothic font, alternating italics and bold between sentences. Would you want to use that in your working paper? In your submitted version?