Decanting is more than just pouring wine into a fancy vessel
This differs greatly from the slow, gentle method used to remove sediment from an older wine. To facilitate this, it is crucial that the bottle be stood upright for a few days before opening to allow the solids to fall to the bottom. Holding a light source underneath the shoulder of the tilted bottle, you can see the flow of wine through it, allowing you to leave the sediment behind. With this motion, unnecessary glugging or bubbling in the bottle is to be avoided.
With older wines, provenance of a particular bottle is of extreme importance. Does the fill level look adequate relative to the age of the wine? Is the color clear? Is it a high-quality, age-able wine that was purchased on release and has been stashed away at cellar temperature for decades? That particular bottle is going to stand up to more oxygen, and blossom in a decanter more reliably than a wine with an uncertain history of storage.
Certain varietals tend to react more favorably to decanting than others, most notably the cabernet family, grenache, syrah, and nebbiolo. These are typically used to produce wines intended for mid-to-long term aging, and the more stuffing a wine has for the long haul, the more likely it’s going to drink tight and closed down upon opening. It’s worth mentioning that white wines often need decanting just as much as reds.