You can now wear the same necklace short or long.
Good tip. Another cool way of doing it is to make actual knots in the chain. Not unlike you shorten lanyards or crocheted chains, this works to shorten the length.
That is true. I like this tip because you can adjust the chain in seconds and wear the same necklace with many different tops.
Putting a knot in your chain is a good way to ruin a good chain. Only do this with costume jewelry. I spent many years as a jeweler repairing karat gold and sterling silver necklaces.