Meaning can be understood without these words. Ellipsis is one of the aspects of language that gives text cohesion.
Example
An example of nominal ellipsis, where a noun phrase is omitted, is 'as it has the last three ( )' and of verbal ellipsis 'Yes, I have ( )'.
In the classroom
Analysis of tape scripts of native speakers is one way of raising learners' awareness of ellipsis. This can then be continued as a controlled practice exercise by asking learners to fill in the gaps by replacing the missing words.
Further links:
https://www.teachingenglish.org.uk/article/teens-listening-skills
https://www.teachingenglish.org.uk/article/how-approach-discursive-writing