So, let's say you are up in front of a class, and you have just passed out copies of a multiple page examination, and you want the students to be sure to check that no pages are missing from their copies. You would say:
a. "ye should check thine copy to make sure it has 5 pages"
or
b. "You should check your copy to make sure it has 5 pages"
If you don't like my example, tell me that you never use a plural you.
If the NIV had been first we'd have an NIVO movement now!
And when you are reading, it is very difficult to know if the speaker is referring to the singular or the plural.
The King James by following the Greek, uses 'Ye' and 'Thee' so that there is no confusion when reading it.
Hence, in John. 3:7, when the Lord said 'Ye' must be born again, He was not speaking only to Nicodomus but to all of us.
If you leave just 'you' there, you could think that He is only talking to Nicodomus, instead of making a general statement.
In fact, the modern versions have to compensate by either having Christ refer to His 'statement' or placing the comment in parenthesis, to show that it is a general statement and not soley directed to Nicodomus.