For showcasing in the media -on camera casting off camera with a scene partner is what is going to be asked of your student in the professional world because reaction is just as important on camera as the speaking of lines. However, for stage work a monologue is important.
Monologues are also used when anyone, usually an agent, ask you to perform your best work on the spot (at an audition or interview).
Cold reading (the ability to break down, understand, bring to life a script while you still have the side in your hand...not so much reading as not fully memorized full performance) is vital in film and television, as it is the most common form of audition.
Reading from a script, teleprompter, cue card or the appearance of using those tools (you can still memorize, but never let them know at an audition that you are not using the tools) are important for commercial on camera, industrial/educational, convention and voice work.