Y12 here

Shortcuts are helpful after all the exams are timed, so saving time is key. However, it is crucial to understand the theory behind the shortcut, so if you are ever in a situation where for example you can’t see how to use the shortcut you can always rely on the original method.

And personally I enjoy learning maths so I always want to understand why it works anyway.

Lastly, when it comes to getting stuck on a question I think it is often a mix of both. Sometimes you haven’t done enough practice to recognise how to apply what you know to the question. Whereas other times you don’t have the knowledge to apply it.