I didn't see it mentioned, but I wonder if Audacity inverts the RIAA equalization curve.
I would guess that the Audacity people assume that people would be using a turntable plugged into a preamplifier with RIAA equilisation built in.
http://midimagic.sgc-hosting.com/mixphono.htm
History before the 1950s is complex. Audacity has provision for defining a frequency response curve and applying that curve to a project.
And on the digital side the ADC makes a noticeable difference. Plus is it isolated from the other circuitry, particularly power supplies?
Ripping vinyl takes enough work, it's worth knowing the few details that make the effort worthwhile.
Most people rip vinyl using a hardware phono stage (which is a preamp + RIAA eq), but there are some audiophiles who prefer to rip using a straight mic pre, which bumps the levels up without applying any eq, and then applying suitable eq in software.
In theory, this would let you play around with different variants of the eq curve, and it would mean not needing a phono stage but only a (cheaper) mic preamp. In practice, most people who rip vinyl are going to have a phono stage anyway, because they want to listen in addition to rip, and there's just not that much benefit of doing it in software vs. using a cheap-but-decent analog phono stage, so few people do.
The exception seems to be people who are into early 78s, which often have proprietary eq curves.
One use the guide mentions is using it in inverted mode, if you want to undo the effects of incorrectly applied RIAA equalization (eg. when a 78 rpm record is being digitized with a different pre-emphasis method).