I’d break it down this way — an Idea worth posting, is worth posting NOW.
I use the phone to bag those little conceptual trophies. Needs a well thought out Title, that’s the only critical part. — Because I automatically echo posts to my other SM channels. So the Title needs to be okay there for a while, sort of stand alone.
Later, after I get back to my desk (and if I can remember) I edit the post, enhance, amplify, drop in an image, etc. — compose tags and categorize. You can bet that it will get crawled for search, but it could be weeks before that happens.
If you want to make the post pretty in Facebook, G+ and all of that — its best to compose in the Site Control Panel, put your images up high in the post so they show in those channel feeds.
But a good idea in text always trumps a mediocre one with lipstick. (at least I think that way.)