Strongly disagree that memorization isn't important. It's THE foundation to be able to do effectively do more advanced stuff.
Take the equation (5678 • 9876). Use long multiplication and you only rely on doing a bunch of single digit multiplications and additions. It's so much faster to be able to instantly know each step instead of having to recalculate these "atomic" steps again and again in your head.
You generally don't need to be able to solve multiplications involving double digits in your head. It's nice-to-have but otherwise useless, as long as you're able to calculate the ballpark of the result.
For example, (38•63) is roughly 2400 and I can then calculate it on paper instead of in my head.
Head calculations are just so much more error-prone than written calculations. Don't do them if you can avoid them. There's a reason why math students (at a university) are infamous for being unable to make the simplest calculations in their head. It takes effort that could be spent somewhere else.