Though, I'd like to add, it might be possible with some cycles that speeds are stepped, so what starts out slow and then might change to higher speeds.
That reduces deep-set wrinkels, and allows the pump to cope with the amount of water which, if not drained fast enough, is whipped up to dense foam by the drum, as murando described.
Wondering there why they wouldn't use such a spin profile for the intermediate spin(s) as better extraction of the soapy water improves rinsing.
On some models and versions, slow isn't slow in another cycle. One might be a few rpm higher or lower then some other.
And, especially on the digital versions, some cycles default to lower spin speeds then are actually selectable, just for care and reduced wear on the machine.
And last but not least, if you want to get the maximum extraction, you can always run a spin only in the end to make sure you get a long high speed spin.
Side note there: With certain thinner items like T-Shirts or socks and underwear, higher spin speeds have a lesser effect on saving time and thus energy in the dryer, simply because they don't hold as much water to begin with. And lower spins speeds there reduce wrinkling, though a dryer will somewhat cancel out the difference in creasing.
With heavier items (towels, jeans, sweatpants or such), they hold more water by nature and thus higher spin speeds have a higher effect.
But I found that with some dryers and loads, I like to spin items which are heavily layered such as jeans (around the pocket areas) at a somewhat lower speed. The higher residual moisture in the single layered areas extends the drying, and as extraction on the multi-layered areas isn't all that good no matter what, the longer drying time allows for better heat penetration in these areas, improving the eveness of drying.
Pair that with low temperatures and some jeans get almost completly evenly dry, even the fith pocket which ususally always stays damp.
But, to give you some numbers from the european market to put extraction rates into perspective:
1400rpm is the average spin speed for a washer here. 1600rpm is the highest currently avaible. There are few 1200rpm models, but the verry bottom of the line goes down to 1000rpm.
Let's take an 8kg load, that is a little more the 17.5lbs.
A 1400rpm machine reaches about 50% residual moisture content, meaning that 50% of the weight of the dry laundry will remain in it as water.
For the example load, that is exactly 4kg, or 4l, which equals just above 1 gallon of water.
The 1200rpm model and the 1000rmp model reach 55% or 60% respectivley. That is 4.4l or 4.8l for each, which is about equal to just above 1.15gal/1.25gal.
The 1600rpm machine however will reach 44% residual moisture, equal to 3.52l, or 0.92gal.
There was this show-off thing manufacturers had in Germany in the early 2000s where everybody offered 1800rpm machines. These reached 42%, equal to 3.36l, or 0.88gal.
So, its 1.25gal->1.15gal->1gal->0.92gal->0.88gal as stepping. You see the biggest jump is from 1200rpm to 1400rpm, so that was the sweetspot to accumulate around. 1600rpm still has a littel advantage versus 1400rpm, but stepping up to 1800rpm barely changes the results.
What the point of this is: There is a certain sweetspot for spinspeeds, where extraction is good, but you don't overwork laundry and machine. People who dry a lot on the line don't care about spin speeds to much, dryer users might want to grab a 1600rpm model.
Each design is pretty unique with that, we in Europe just have the advantage of drumdiameters not changing to much between manufacturers and machines, so the spin speed usually determines the extraction in percent by almost direct correlation.
With US machines, and the high dryer use, something simmilar to a 1600rpm would be a good grab, but as tub sizes vary a lot between machines, 2 machines with the same spin speed can have vastly different extraction rates. And as spin-speeds in the US for the most part are lower then those in the EU, the difference between slow and fast might not be all that big, or at least not significant enough to actually affect the drying time much.
