On some machines, the "stain" function now means a soak (no agitation) at the set wash temperature in the middle of the wash cycle. My somewhat vintage Frigidaire 2140 (four years old but design is about six years old) has a separate Soak cycle. You use half a dose of detergent, it soaks them in cold water for like half an hour with minimal agitation, then spins them out. Cycle is over and now clothes can be put through a wash cycle with full detergent dose. (you have to set up the second cycle yourself, it won't go from Soak to Wash automatically). Fancier machines have had similar Prewash cycles that dose the correct amount of soap from a separate dispenser compartment, then they advance automatically to the wash cycle.
The trend seems to be away from Soak or Prewash cycles, because they involve an extra fill/rinse and use additional soap. The current line of Frigidaire Affinity machines (considered more upscale than my 2140 or the higher end 2940) no longer have the Soak cycle. Instead, there is a Stain Clean option which provides 6-12 minutes of no-agitation soaking within the wash cycle. No separate soap compartment, and no prewash/soak in which the machine fills, soaks, drains, spins out, and then begins a full wash cycle.
From experience, I know that my Soak cycle works VERY well. I have saved dress shirts with ink stains from leaking pens using Soak cycle and Persil or equivalent. If my machine died today and I replaced it with another Frigidaire (I have a stacked configuration and only a Frigidaire washer below would allow re-use of the gas dryer), I'd have to think twice whether to move up to an Affinity or use a 2940, which still has the Soak cycle (if I had to choose again, I would get a 2940 over a 2140 because it offers Auto Temp Control and variable delay wash, vs. 2140's lack of ATC and only a fixed 8-hour delay wash, which can be turned on or off). The Soak cycle is useful now and then, so fans of the feature might avoid Affinity for this reason.
FYI, I received a water rebate on my 2140 in 2006, but today it would not qualify because it does not meet Tier 3 water efficiency. Some of the Affinity's do meet the requirement, as does Electrolux. This tells me that 2140/2940 use more water, which may explain why owners are generally pleased with their cleaning ability, and why 2940 has ranked among the top three choices on Consumer Reports' ratings for four years in a row.
(CR does not test long term durability, so you take their ratings with a grain of salt, but their evaluations of cleaning ability are reasonably accurate. They also consider price when making their "Best Buy" recommendations, so a washer like the 2940 @$650 will beat washers @$1000-1200 that clean the same or only marginally better, even if the pricier washers have features that some buyers would prefer or need).