As with any hobby or vocation, in knitting there are various levels of proficiency from beginner to expert.
As an Absolute Beginner I found that I didn't really "think" about knitting very much at all. I just got a pattern, the yarn required for it and went at it. I never saw the value of the swatch and so didn't do one. I got lucky. There were never any sizing woes despite not doing a swatch.
Then, in the Intermediate Beginner stage, I said, "Oh! So that's why they tell you to do a swatch," but I only rarely did it and problems occurred. Again, not hugely problematic, but I started to actually be aware of the issues. At this stage I also began reading charts and had most of the standard lingo down pat.
When I hit the Advanced Beginner stage I did my swatches regularly, thus got gauge regularly and could pick up just about any pattern and get through it. Charts were no problem and neither were lace or cables.
I would classify myself now as an Intermediate Knitter. I'm starting to tackle the Why's and Wherefore's of my chosen favorite hobby. (Notice I said favorite. You have no idea how many hobbies I have. I'm a chronic hobbyist.) I can now modifiy patterns on the fly and even create some basic ones. But I still feel like a fledgling just learning to flex it's wings. You know you've hit the intermediate stage in any endeavor when you say to yourself "I'm really good at this!" and then are brought crashing down to reality and are humbled by how much you still have to learn.
Case in point: I drew up a sketch of a sweater that I want to create. I was good and made swatches of the various patterns that I want in it, mainly to check my gauge and to do all the math-y things that are required when creating. However, I learned so much more this time from my swatches than I expected to.
On my stockinette swatch, using 100% wool, I went up a couple of needle sizes and got a fabric that is a little less dense and therefore has more drape and really liked it. It's not so loose that it has gaping holes, but the fabric is not stiff either.
The cable swatch, done on the same needle size was done mainly to test that I could do the cable and that worked a treat too.
But where I ran into problems was at the bottom of the sweater. I wanted a textured stitch for more interest. I wanted something beyond garter, ribbing, seed or moss stitch that wouldn't curl. I thought that I had found the perfect stitch pattern for it. Again, using the same needle size, I swatched it up and was all proud of myself, but what I got, I didn't really expect. Yes, it's beautiful and doesn't curl a bit. Yay for that. However, my fabric came out far more dense than expected.
Here's the two swatches side by side:
The one on the right almost has the denseness of crochet. There's no fluidity at all to the swatch. A little too sturdy for the project that I have in mind. Does anyone want a dense fabric with very little give to it sitting right on their hips and adding bulk? No, I don't think so. Back to the drawing board for me. I'm now off to hunt a new stitch pattern that fulfills my needs a bit better.
Lesson learned: Sometimes the value of the swatch is not just in the gauge that it gives you. It's what it can tell you from a design standpoint; How will a certain type of yarn perform in a given situation. Is it stiff? fluid? have more/less drape? Does the pattern complement or take away from other elements in the design? These are so important to know. It's amazing the information that can be gathered in just a four inch square of knitting.