Why decant wine?
Two main reasons: to get some oxygen into the wine allowing it to flex its muscles or to get rid of any sediment in the bottle. The latter is less necessary nowadays, wines are usually filtered prior to bottling but the former is often a game changer for many wines.
Have you ever noticed a wine that tastes better on your second glass? It's not just the booze talking, often it's because the oxygen has got into the bottle.
Oxygen = magical changes in the wine.
If you give nimble fingered oxygen a chance to massage the wine, it to will allow it to relax, 'breathe' and open up. Just removing the cork and letting the wine sit in the bottle for a while won't do much, because the amount of oxygen touching the wine is limited.
Which wines are worth decanting?
Anything that has some complexity: be it a bold tannic structure; oak aging; high amounts of acidity; lots of body, which is usually due to high amounts of alcohol; layers of varied aromas like fruit, flowers, spice etc; a bit of age, say three years old or more.
Sidenote! Don't let 'ole red take all the glory. Decant your epic whites, roses and sometimes, even, your sparkles too.
How long you decant can really vary on the wine. A Chianti wine maker I met said he allows the wine to sit decanted for 20 minutes every year it has been in the bottle (e.g. a 2015 wine should sit for 5 x 20 minutes = 1 hour 40 mins)
Some Madeiras are said to need two weeks...
If you're not sure, ask your local wine merchant or ping me a message.
Don't have a decanter - it's all good! Use a jug or large bowl.
Strapped for time? Just double decant: like in the video, this is pouring the wine out of the bottle then pouring it back in. Even this will help the wine spread its wings.
And asides from all that, enjoy the ceremonial moment of spending some quality time with your dear friend and loyal lover, Wine.