We've all heard it: "When all you have is a hammer, everything looks like a nail." It's sort of true, though. One thing I've realized as I worked more with hand tools, and which I've mentioned before, is that a lot of things are simpler. Not necessarily easier, but simpler.
I was just reading someone's blog posts about making a "Milkman's Bench", and they were talking about needing to be sure the grooves they milled for the tail vise were exactly 1/2". "Why?", I thought. "Just cut the tenons on the moving part once you've done the grooves, and the exact size won't matter at all!" Except that's harder with power tools. If you're cutting your tenon with a dado stack, you need to know exactly how high to set the blade, or you'll run into trouble.
In a different post, they were thickness planing to make sure that the pieces were exactly 1 5/8" thick. "Why?", I asked myself again. Well, because the parts are being made from a cut list. If you're cutting everything from a list, then doing assembly, it's a lot easier to make sure everything is identical before you start doing assembly. In non-machine work, it's kind of irrelevant what the actual size of any of the parts is, because it's trivial to just size each piece to fit the one before. Maybe you end up at 1 11/16", or 1 7/8", but it doesn't really matter.
For me, it's now easier to treat dimensions as a guideline, an ideal that I don't really need to achieve unless I'm building a piece of furniture to fit a specific space. Other than that... So what if I'm a few sixteenths off? I'm going to plane everything flush when I'm done anyway.
Now, please don't get me wrong. This isn't a condemnation of power tools, or a statement that people are in some way "wrong" for building to exact dimensions. If you're using power tools, it really is a better/easier way to work. I think a lot of hand tool workers would be baffled by the idea of cutting everything to exact tolerances, and the power tools folks would be baffled by our failure to measure anything precisely. Neither way is better.
The point is that the tools we use determines how we think about things, and how we approach problems.