Given the advantages of making a glide -- adding harmony and interest -- and no disadvantages, it is interesting to find places where no glide is the best interpretation.
Notes with Emphasis
There is a tune to sing the Lord's prayer. The highest note is on "ev" (in the word "forever"), and it is in a sense the climax of the song. I have heard this done with and without a glide. It is electrifying without the glide; the glide disappointed. This is unfortunate for the poor singer -- this is not an easy note to hit, and it would help if the singer could glide into it.
Presumably this has something to do with the emphasis, which is achieved by a sudden increase in loudness. When should the sudden increase in volume occur if there is a glide? Logically, there is no good place for this. So, to speculate, perhaps an emphasized note cannot receive a glide because the emphasis has to occur at the start of the note and on the right note, not the glide.
If the climatic "ev" is not emphasized by loudness, then I think a glide works out fine. Of course, then the effect is very different. (IMO, emphasizing "ev" goes better with what comes before, and not emphasizing it makes the ending better. The song might work best with a Lutheranesque "forever and ever" instead of just "forever".
In the song "Somewhere Over the Rainbow", the interlude is a Bach-like repetition of notes on "some day I'll wish upon a star". I have never heard this done well with gliding. I have heard it performed with gliding, and it did not sound good.
I speculated on why. Perhaps it is because Bach-like things shouldn't have glides.
But another possibility is that this sounds bad only when the glides are all the same to a repeating note. As noted elsewhere, when a not repeats, the glides should be different. In "some day I'll wish upon a star", there are four repetitions of the top note. If there are glides on the second and fourth, it sounds fine to me.