For the last 3 or 4 years most of my knitting has been done on 2.38 mm (~ US#1) needles. Now, after much swatching and soul searching, I have moved onto 1.5 or 1.6 mm needles (~US# 000). I note that all of my current knitting is being done on 1.63 mm gansey needles (knitting pins) and 1.98 mm swaving pricks (which produces a similar gauge for me.)
If I knit on the 1.6 mm needles with gansey yarn, I get ~ 11 spi . If I knit on the 2.38 mm needles I get ~8 spi with standard commercial gansey yarn. That means that the fabric knit on the finer needles is much denser and warmer -- despite being much thinner and lighter. This goes beyond what I have been knitting. Thus, we enter into the glory that is fabrics knit on "knitting pins". Yes, now I am knitting sweaters on 14" long US 000 needles. Current knitting projects are a gansey for myself from 6-ply @ 1680 ypp and socks from 5-ply @ 1000 ypp. And, there is an order for a pair of fine gloves
(On a recent trip back East, TSA allowed a set of 6 x 1.6 mm x 25 cm lace needles in my carry-on baggage in a clear plastic tube without comment. Frankly, I think those needles are "pointy" and should not be used anywhere people sit close together.)
The other night at the dinner table, I was sitting across from a knitter with 60 years of experience. She has daughters that knit, so the cumulative knitting experience of the family is more than 100 years. She thought the (1.6 mm) needles that I was using were too flexible. I was using them for the gusset of a sock being swaved from commercial 5-ply gansey yarn. I like swaving on aircraft. It is fast, ergonomic, and the needles are blunt, compact, and do not roll away if dropped.
In these socks the ankle and foot are swaved and the heel gusset and toe are knit on the DPN, because swaving produces fast, easy tubes, and the DPN are easier for decreases. Thus, most of the sock is swaved, and I use DPN just for the gusset and the toe.
As the conversation continues, it turns out that the Senior Knitter had never knit a fabric as dense as what I was knitting, nor even, had she ever knit socks. (Her daughters knit socks, but not that tight.) And, she thought the sport weight yarn I was using was "awfully thin". (It was worsted spun so it has less volume than the synthetic yarns she uses).
This set me to thinking. For knitting tight fabrics, I like the most flexible needle that will knit a fabric at the firmness that I desire. The more flexible needle is easier on the hands. The knitter across from me likes aluminum needles at that gauge. I have bins of such needles, but I packed the SS needles into the project bag because they were stiff enough, but easy on the hands.
Basically, she likes the flex of her aluminum knitting needles, and I can understand that. However, I do not know which needles I want for a particular project until I have done a set of swatchs and compared the performance of all of the potential needles. The winner of the recent comparisons was the hollow SS needles used with a Shetland knitting belt. Tubular needles used with a knitting sheath do tend to crimp and collapse, and I have said this before, and likely will say it again. Tubular needles tend to be more fragile. If I was a serious knitter, I would always use the solid spring steel needles because I know they are more durable. I have no confidence that these tubular needles will endure to knit more than a few ganseys.
No, I do not "just know from experience" which needle is better because I do not do the same project over and over. I try to make each project better, faster, and cheaper. I do not have a stack of the same objects differing only by color. However, with 60 years of knitting, she knew just from experience that those needles were too flexible. I have moved from the spring-steel lace needles to the hollow stainless steel needles because they produce a similar fabric, and the more flexible needles are lighter and less likely to fall out of loose fabrics.
If I were a serious knitter, I would only knit with the solid spring-steel needles because they endure, and that is a virtue for the serious knitter. I doubt if any of the the tubular SS needles would endure to knit more than a few ganseys. Those blankets are more loosely knit, the tubular SS needles will easily knit hundreds or even thousands of such objects. However frankly if I was knitting so loosely, I would just use bamboo needles.
But I digress. "Knitting pins", produce a qualitatively different fabric. It is a lot of work, but the results are impressive. No amount of "tight knitting" with bigger needles will produce the same results. At one time there was a whole industry built on such knitting with very fine needles. They did not do it for fun, they did it because it produces a wonderful fabric. Try it.
Confucius say, "Only one who attempts the absurd can achieve the impossible."