I can't say that you "need" to decant the wine, but I certainly would. The sediment can cloud the wine and often imparts a bitter taste, and the gunk and grit is just nasty stuff. Even if the bottle has been left upright to allow the sediment to settle, serving it without decanting tends to stir it up, which can affect the last third or more of the bottle.
Decanting is very easy, despite the ritual that often surrounds it in the movies, and you do not need a fancy decanter. Here are the basics, at least as I've come to do it over the last 35 years:
1. Leave the bottle upright for at least 24 hours, preferably 48 or more.
2. Carefully cut off the top of the foil and extract the cork, being careful not to move or shake the bottle anymore than necessary.
3. Gently lift the bottle and pour the wine slowly into a suitable glass container -- I prefer a 4-cup Pyrex kitchen measuring cup, which easily holds a 750ml bottle.
4. While you're pouring, you need to observe the wine in the neck of the bottle; I used to use a candle for that purpose (like in the movies), but a few years ago I discovered that my pocket Maglite works as well with less fuss -- I just hold it under the bottle, against the neck as I pour.
5. When you start to see sediment in the wine, slow the pour to a trickle, stopping entirely when the sediment get to be significant. There should be no more than an ounce or two left in the bottle, although sometimes you will have significantly more, sometimes almost none.
6. Pour the few ounces of wine and gunk remaining in the bottle into a glass if you intend to drink it, or down the drain if not. (See comment below.)
7. If you're not using a decanter to serve the wine, rinse the now-empty wine bottle a couple of times to remove any remaining sediment and gunk. Don't worry about any dark stain on the side of the bottle -- if it doesn't some off with rinsing, it's not going to affect the wine. I then rinse the bottle with filtered water, although that's probably overkill unless you're dealing with something expensive. Shake out as much water as possible from the bottle, and pour the wine from the Pyrex cup back into it -- this is called "double decanting" and further aerates the wine.
8. As for the the last bit of wine you poured into a glass, you can try removing the sediment and gunk with a coffee filter, which will get out the heavy grit but leave the wine cloudy, or a paper towel, which does a better job of removing the cloudiness but may affect the taste. This last little bit of wine is drinkable, but don't add it to the decanted wine -- have it yourself.
That's about it. With practice, you can do this in a minute or two, and it will greatly enhance your enjoyment of the wine.