The NKJV does update some of the archaic language to our more modern vernacular. It also makes some improvements on the translation.
You may not know this, but the word ‘prevent’ had different meaning in 1611 than it does today. A modern person reading the KJV would most likely miss that.
Scholarship since 1611 has learned more about how the Greek grammar is constructed. An example of this would be the Granville Sharp rule.
Titus 2:13
Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ (KJV)
Looking for the blessed hope and glorious appearing of our great God and Savior Jesus Christ (NKJV)
Notice how the NKJV makes use of this by rendering the verse with more clarity on the deity of Christ.
I think the included footnotes in the NKJV are excellent for examining basic textual criticism and offer alternate translations of a particular word.
Colossians 2:8
Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ. (KJV)
Beware lest anyone [
a]cheat you through philosophy and empty deceit, according to the tradition of men, according to the basic principles of the world, and not according to Christ. (NKJV)
a. Lit.
plunder you or
take you captive
The word “spoil” in the KJV is the more accurate translation. However, I think the NKJV does make this verse read more smoothly by changing it to “cheat” and does include a footnote for you to consider the literal definition of the word.
As far as I can tell, the only real advantage to using the KJV over modern translations is the distinction of singular and plural pronouns (the thees and thous).