Motion designers, know the expressions?

Question

Design

Question for motion designers or those who are familiar with motion design and can explain about motion design.
Do you remember the expressions by heart?
Without knowledge of expressions, it will be hard in motion design with after effects?)
For example, there are harmonic vibrations of roughly a square, I can do it with keys, but it can also be done with an expression, besides saving time, what else do expressions give?
I haven't come across anything complicated in motion design yet (I'm still learning)

Answer 1

Saving time is the main thing + some features that cannot be done differently in AE.