On the other hand.......a lot of unacompanied singers do shorten the long notes, sometimes radically, in certain songs, which, to my mind anyway, can throw out the whole rhythm and cadence of a song. By all means, "make a song your own" but don't lose the natural flow of it.
And on the third hand, if singing unaccompanied, you can make more sense of the words by using a bit of good old rubato (varying speed), proper phrasing, NOT singing to a click-track in the ears, etc.
If the above statements sound contradictory, I know what I mean, even if you don't!