Difference between "Please don't be long" and "Please don't YOU be long"

In the song "Blue Jay Way" from the Beatles, we've got the following lyrics :

Please don't be long

Please don't you be very long

I'm (obviously) not a native English speaker but the first sentence seems right to me but the second one seems pretty weird because of the subject of the imperative sentence being explicitly given.

Is the second one just as right as the first one? Is it just a songwriter trick to get the good number of syllables? Is it something specific to the scouse?

Does having an explicit "you" change anything in the meaning? Which one is the most usual?

(Also, one can find the same king of difference in "Don't ever change" :

So please don't ever change

Now don't you ever change )

Adding "you" to such a request simply adds an extra measure of personal emphasis. It's in effect saying, "Hey, look at me. I'm telling you not to be very long." The speaker may feel the emphasis is needed in case the listener is not paying close enough attention. It's common to use such constructions with children.

Don't you ever touch Mommy's pills again. You could get very sick.

So, there are two things achieved with this: one poetic, one rhythmic.

Poetic: by changing it up from line one to line two is the sense of "belong" as in 'inclusion' in the first line, while the second line is clearly and literally "don't be long" as in "don't be late / tardy / not on time"

So "please don't be long" or I may be asleep (If you're like everyone else, I may get bored) & "please don't be long" or I may be asleep (If you're late, I may fall asleep)

Rhythmic: the second line takes the melody of the first line and inserts a tuplet (irregular rhythm) over the "you" in the second line: please don't be long (4) / please don't you be ve-ry-lo-o-ong (9) / please don't be long (4) / or I may be a-slee-eep (7)

So it goes regular / irregular / regular / irregular (because of the triplet on asleep in line 4). I think this is pretty accurate... its some really great songwriting. Like "Got to Get You Into My Life," this is an early example of the Indian influence on the Beatles--the irregular rhythms in these lines also are sung melismatically (as opposed to syllabic)

Compare against "Long, Long, Long" - another great George Harrison-penned Beatles song.