A Song Is A 'Communication'.
Even an instrumental composition attempts to 'communicate' the 'feel' or 'emotion' implied in the music.
A Lyric is comprised of words with meanings, so the Singer 'sends' those words.
To fully qualify as a 'communication' the words have to be 'received'.

That Latin prefix, 'com', means 'with', implying the 'sender' and the 'receiver'. We communicate 'with' one another.

If the words are 'sent' but not 'received' the 'sender' didn't 'communicate with' the intended 'receiver'.

The Lyric has to be intelligible, not too obscure, although obscurity can work to some degree. Obscurity in poetry differs in that the reader can re-read. A Lyric has to communicate the first time, as heard.

The Lyric has to be enunciated, so the word meaning is not sacrificed to the Note execution.
A voice has to take on the characteristics you would find in an instrument executing Notes but retaining the characteristics of a Human voice 'communicating' word meanings.

If the Singer fails to 'send' to effectively communicate a single word the 'receiver' may assume what the word is by the context, and by the Rhyme if it is a Rhyme-Word. If not, missing that word, or a couple words, may keep the Line from communicating.
Failure of a Line to communicate may keep the Stanza (Verse or Chorus, e.g.) from communicating.
Soon the whole Song may fail to communicate because of the 'values' of those missed words.

Listeners can focus their attention, study a little harder, 'listen up', pay attention, replay, but ideally, you want to 'send' so they have no option but to 'receive', and receive the first time they hear it.
Your product has Hook Factor, something that hooked you, The First Listener, and should hook other listeners, and keep them hooked as you 'communicate' your Lyric. If you lose them at any point, especially early in the Song, you may not get them back.

I suspect Bob Dylan's enunciation, a subject of like/dislike discussion for many years, is a product of his listening to the playback and realizing some words weren't being received, and so he re-cut the recordings and sent those words more deliberately.

It may be difficult for a singer to evaluate the 'sending' qualities. They KNOW the words.

I suspect sometimes it is a matter of a singer sustaining a note until it 'slides' into the next note, something an instrument might do, and even spoken might have that effect. But each word must be given its space, and not 'sounded' in a manner too different from how it would be spoken.

Note Dolly Parton's classic, "I Will Always Love You". That title Line is sung pretty much the same way as it would be spoken. The word "I" gets a multi-note delivery, and "you" is sustained a bit. But basically, the Line is 'sent' as it would be spoken, and is easily 'received' the first time you hear it. It communicates.

Strother Martin, a character actor, in the movie "Cool Hand Luke", delivers a 'catch-phrase',
"What we have here is a failure to communicate."
Don't have a failure to communicate.

There will always be another song to be written. Someone will write it. Why not you? www.garyeandrews.com