The second reason is that the hard lessons are the ones that stick. I don’t want to have to re-work anything if I goof, so it behooves me to think things through. On the computer, it’s easy to draw things, so you don’t need to visualize, and it’s easy fix things, so there’s less incentive to pay attention. CAD makes it too easy to be sloppy.
Drafting programs make quick, clean drawings, but the accuracy is derived from the computer. When you go to the bench, the quality of your work is derived from your own attentiveness and care. And that’s huge. Drawing by hand engages the 'real, physical' part of the mind in a similar way to working with wood. It's a mentality builder, because you have to train your mind to visualize what you’re making ahead of time, and to execute that vision with care. That’s a mentality worth fostering, because it will really cut down on mistakes at the bench. The joke we used to make at school was: “Save a tree: Waste all the paper you need to.”
Thankfully, there are some really nice tools out there right now, for short money, that can encourage the process of learning.
I've been on a vintage drafting tool kick recently. What I've realized lately is that really, really nice vintage tools, tools that clearly have a history and a soul, are going for pennies on the dollar. Well, it may actually be pennies on the original pennies, given inflation, but they were clearly made to a much higher standard, and are remnants of a day when drafting was a serious trade of its own.
These are tools from over a hundred years of a serious profession, that have basically been dropped off at the flea market. Tools that were made with intent, and without patches or upgrades, are swimming in the purgatory of eBay, waiting to be useful again, even if the sellers don't always know what they're actually for. This is great for guys like me who can now afford really, really nice tools to draw with.
That said, it's a little depressing to think about. I'm working with tools that were made by people who took drawing seriously, in an age when most serious 'artists' are using computers. And it's getting to the point where some of them don't even know how to draw by hand. In short, the tools are evidence of human potential that used to be highly developed... and that we now choose not to foster... despite the advantages that it has to offer.
*Another tip from the vintage drafting book, draftsmen used to lubricate the pivot points of their compasses with hot bees wax. I gave it a try, just to see for myself. Unlike paraffin, beeswax is just a little bit sticky. It still glides smoothly, but it holds the setting of a set of dividers, for instance, very well. Much better than I'd have thought. It was another of those 'who knew?' kind of things for me. (Who knew? Professional tradesmen who drafted for a living, that's who.) It's been a game changer.