We do it with old wines to make the volatile alcohlic part evaporate, so you can totally enjoy the nose experienceI do the opposite, generally speaking. If it's a younger wine that is tannic and big like a Bordeaux's, Cabernet Sauvignon, Bolgheri or a Primitivo I'll aerate to soften the tannins and easier to drink because the wine is still pretty tight and for an older aged wine of that same varietal I might not. An aged wine can go flat really really fast with too much oxidation, so I'm generally less likely to do that, but when I do it gets consumed quickly in other words it's not sitting in the decanter for very long and it helps with the sediment. Light bodied ready to drink reds like Gamay, Pinot's and Nebbiolo's or a Lambrusco's I won't decant, generally speaking.
and for the sediment, of course
for the younger ones, in my taste, is sufficient some minutes in the proper glass...
for the conservation I don't know...I'm in the I am part of the group of those who when they open a bottle they finish it, at most from dinner lasts until lunch the next day: D